redis - a node.js redis client

This is a complete and feature rich Redis client for node.js. It supports all
Redis commands and focuses on high performance.

Install with:

npm install redis

Usage Example

var redis = require("redis"),
    client = redis.createClient();

// if you'd like to select database 3, instead of 0 (default), call
// client.select(3, function() { /* ... */ });

client.on("error", function (err) {
    console.log("Error " + err);
});

client.set("string key", "string val", redis.print);
client.hset("hash key", "hashtest 1", "some value", redis.print);
client.hset(["hash key", "hashtest 2", "some other value"], redis.print);
client.hkeys("hash key", function (err, replies) {
    console.log(replies.length + " replies:");
    replies.forEach(function (reply, i) {
        console.log("    " + i + ": " + reply);
    });
    client.quit();
});

This will display:

mjr:~/work/node_redis (master)$ node example.js
Reply: OK
Reply: 0
Reply: 0
2 replies:
    0: hashtest 1
    1: hashtest 2
mjr:~/work/node_redis (master)$

Note that the API is entirely asynchronous. To get data back from the server,
you'll need to use a callback. From v.2.6 on the API supports camelCase and
snake_case and all options / variables / events etc. can be used either way. It
is recommended to use camelCase as this is the default for the Node.js
landscape.

Promises

Native Promises

If you are using node v8 or higher, you can promisify node_redis with util.promisify as in:

const {promisify} = require('util');
const getAsync = promisify(client.get).bind(client);

now getAsync is a promisified version of client.get:

// We expect a value 'foo': 'bar' to be present
// So instead of writing client.get('foo', cb); you have to write:
return getAsync('foo').then(function(res) {
    console.log(res); // => 'bar'
});

or using async await:

async myFunc() {
    const res = await getAsync('foo');
    console.log(res);
}

Bluebird Promises

You can also use node_redis with promises by promisifying node_redis with
bluebird as in:

const redis = require('redis');
bluebird.promisifyAll(redis);

It'll add a Async to all node_redis functions (e.g. return client.getAsync().then())

// We expect a value 'foo': 'bar' to be present
// So instead of writing client.get('foo', cb); you have to write:
return client.getAsync('foo').then(function(res) {
    console.log(res); // => 'bar'
});

// Using multi with promises looks like:

return client.multi().get('foo').execAsync().then(function(res) {
    console.log(res); // => 'bar'
});

Sending Commands

Each Redis command is exposed as a function on the client object.
All functions take either an args Array plus optional callback Function or
a variable number of individual arguments followed by an optional callback.
Examples:

client.hmset(["key", "test keys 1", "test val 1", "test keys 2", "test val 2"], function (err, res) {});
// Works the same as
client.hmset("key", ["test keys 1", "test val 1", "test keys 2", "test val 2"], function (err, res) {});
// Or
client.hmset("key", "test keys 1", "test val 1", "test keys 2", "test val 2", function (err, res) {});

Care should be taken with user input if arrays are possible (via body-parser, query string or other method), as single arguments could be unintentionally interpreted as multiple args.

Note that in either form the callback is optional:

client.set("some key", "some val");
client.set(["some other key", "some val"]);

If the key is missing, reply will be null. Only if the Redis Command
Reference states something else it will not be null.

client.get("missingkey", function(err, reply) {
    // reply is null when the key is missing
    console.log(reply);
});

For a list of Redis commands, see Redis Command Reference

Minimal parsing is done on the replies. Commands that return a integer return
JavaScript Numbers, arrays return JavaScript Array. HGETALL returns an Object
keyed by the hash keys. All strings will either be returned as string or as
buffer depending on your setting. Please be aware that sending null, undefined
and Boolean values will result in the value coerced to a string!

Redis Commands

This library is a 1 to 1 mapping to Redis commands.
It is not a cache library so please refer to Redis commands page for full usage
details.

Example setting key to auto expire using SET command

// this key will expire after 10 seconds
client.set('key', 'value!', 'EX', 10);

API

Connection and other Events

client will emit some events about the state of the connection to the Redis server.

"ready"

client will emit ready once a connection is established. Commands issued
before the ready event are queued, then replayed just before this event is
emitted.

"connect"

client will emit connect as soon as the stream is connected to the server.

"reconnecting"

client will emit reconnecting when trying to reconnect to the Redis server
after losing the connection. Listeners are passed an object containing delay
(in ms from the previous try) and attempt (the attempt #) attributes.

"error"

client will emit error when encountering an error connecting to the Redis
server or when any other in node_redis occurs. If you use a command without
callback and encounter a ReplyError it is going to be emitted to the error
listener.

So please attach the error listener to node_redis.

"end"

client will emit end when an established Redis server connection has closed.

"drain" (deprecated)

client will emit drain when the TCP connection to the Redis server has been
buffering, but is now writable. This event can be used to stream commands in to
Redis and adapt to backpressure.

If the stream is buffering client.should_buffer is set to true. Otherwise the
variable is always set to false. That way you can decide when to reduce your
send rate and resume sending commands when you get drain.

You can also check the return value of each command as it will also return the
backpressure indicator (deprecated). If false is returned the stream had to
buffer.

"warning"

client will emit warning when password was set but none is needed and if a
deprecated option / function / similar is used.

"idle" (deprecated)

client will emit idle when there are no outstanding commands that are
awaiting a response.

redis.createClient()

If you have redis-server running on the same machine as node, then the
defaults for port and host are probably fine and you don't need to supply any
arguments. createClient() returns a RedisClient object. Otherwise,
createClient() accepts these arguments:

• redis.createClient([options])
• redis.createClient(unix_socket[, options])
• redis.createClient(redis_url[, options])
• redis.createClient(port[, host][, options])

Tip: If the Redis server runs on the same machine as the client consider
using unix sockets if possible to increase throughput.

Note: Using 'rediss://... for the protocol in a redis_url will enable a TLS socket connection. However, additional TLS options will need to be passed in options, if required.

options object properties, Property, Default, Description, -----------, -----------, -------------, host, 127.0.0.1, IP address of the Redis server, port, 6379, Port of the Redis server, path, null, The UNIX socket string of the Redis server, url, null, The URL of the Redis server. Format: [redis[s]:]//[[user][:password@]][host][:port][/db-number][?db=db-number[&password=bar[&option=value]]] (More info avaliable at IANA)., parser, javascript, Deprecated Use either the built-in JS parser javascript or the native hiredis parser. Note node_redis < 2.6 uses hiredis as default if installed. This changed in v.2.6.0., string_numbers, null, Set to true, node_redis will return Redis number values as Strings instead of javascript Numbers. Useful if you need to handle big numbers (above Number.MAX_SAFE_INTEGER === 2^53). Hiredis is incapable of this behavior, so setting this option to true will result in the built-in javascript parser being used no matter the value of the parser option., return_buffers, false, If set to true, then all replies will be sent to callbacks as Buffers instead of Strings., detect_buffers, false, If set to true, then replies will be sent to callbacks as Buffers. This option lets you switch between Buffers and Strings on a per-command basis, whereas return_buffers applies to every command on a client. Note: This doesn't work properly with the pubsub mode. A subscriber has to either always return Strings or Buffers., socket_keepalive, true, If set to true, the keep-alive functionality is enabled on the underlying socket., socket_initialdelay, Initial Delay in milliseconds, and this will also behave the interval keep alive message sending to Redis., no_ready_check, false, When a connection is established to the Redis server, the server might still be loading the database from disk. While loading, the server will not respond to any commands. To work around this, node_redis has a "ready check" which sends the INFO command to the server. The response from the INFO command indicates whether the server is ready for more commands. When ready, node_redis emits a ready event. Setting no_ready_check to true will inhibit this check., enable_offline_queue, true, By default, if there is no active connection to the Redis server, commands are added to a queue and are executed once the connection has been established. Setting enable_offline_queue to false will disable this feature and the callback will be executed immediately with an error, or an error will be emitted if no callback is specified., retry_max_delay, null, Deprecated Please use retry_strategy instead. By default, every time the client tries to connect and fails, the reconnection delay almost doubles. This delay normally grows infinitely, but setting retry_max_delay limits it to the maximum value provided in milliseconds., connect_timeout, 3600000, Deprecated Please use retry_strategy instead. Setting connect_timeout limits the total time for the client to connect and reconnect. The value is provided in milliseconds and is counted from the moment a new client is created or from the time the connection is lost. The last retry is going to happen exactly at the timeout time. Default is to try connecting until the default system socket timeout has been exceeded and to try reconnecting until 1h has elapsed., max_attempts, Deprecated Please use retry_strategy instead. By default, a client will try reconnecting until connected. Setting max_attempts limits total amount of connection attempts. Setting this to 1 will prevent any reconnect attempt., retry_unfulfilled_commands, false, If set to true, all commands that were unfulfilled while the connection is lost will be retried after the connection has been reestablished. Use this with caution if you use state altering commands (e.g. incr). This is especially useful if you use blocking commands., password, null, If set, client will run Redis auth command on connect. Alias auth_pass Note node_redis < 2.5 must use auth_pass, db, null, If set, client will run Redis select command on connect., family, IPv4, You can force using IPv6 if you set the family to 'IPv6'. See Node.js net or dns modules on how to use the family type., disable_resubscribing, false, If set to true, a client won't resubscribe after disconnecting., rename_commands, null, Passing an object with renamed commands to use instead of the original functions. For example, if you renamed the command KEYS to "DO-NOT-USE" then the rename_commands object would be: { KEYS : "DO-NOT-USE" } . See the Redis security topics for more info., tls, null, An object containing options to pass to tls.connect to set up a TLS connection to Redis (if, for example, it is set up to be accessible via a tunnel)., prefix, null, A string used to prefix all used keys (e.g. namespace:test). Please be aware that the keys command will not be prefixed. The keys command has a "pattern" as argument and no key and it would be impossible to determine the existing keys in Redis if this would be prefixed., retry_strategy, function, A function that receives an options object as parameter including the retry attempt, the total_retry_time indicating how much time passed since the last time connected, the error why the connection was lost and the number of times_connected in total. If you return a number from this function, the retry will happen exactly after that time in milliseconds. If you return a non-number, no further retry will happen and all offline commands are flushed with errors. Return an error to return that specific error to all offline commands. Example below., ```js

var redis = require("redis");
var client = redis.createClient({detect_buffers: true});

client.set("foo_rand000000000000", "OK");

// This will return a JavaScript String
client.get("foo_rand000000000000", function (err, reply) {
console.log(reply.toString()); // Will print OK
});

// This will return a Buffer since original key is specified as a Buffer
client.get(new Buffer("foo_rand000000000000"), function (err, reply) {
console.log(reply.toString()); // Will print <Buffer 4f 4b>
});
client.quit();

retry_strategy example

```js
var client = redis.createClient({
    retry_strategy: function (options) {
        if (options.error && options.error.code === 'ECONNREFUSED') {
            // End reconnecting on a specific error and flush all commands with
            // a individual error
            return new Error('The server refused the connection');
        }
        if (options.total_retry_time > 1000 * 60 * 60) {
            // End reconnecting after a specific timeout and flush all commands
            // with a individual error
            return new Error('Retry time exhausted');
        }
        if (options.attempt > 10) {
            // End reconnecting with built in error
            return undefined;
        }
        // reconnect after
        return Math.min(options.attempt * 100, 3000);
    }
});

client.auth(password[, callback])

When connecting to a Redis server that requires authentication, the AUTH
command must be sent as the first command after connecting. This can be tricky
to coordinate with reconnections, the ready check, etc. To make this easier,
client.auth() stashes password and will send it after each connection,
including reconnections. callback is invoked only once, after the response to
the very first AUTH command sent.
NOTE: Your call to client.auth() should not be inside the ready handler. If
you are doing this wrong, client will emit an error that looks
something like this Error: Ready check failed: ERR operation not permitted.

backpressure

stream

The client exposed the used stream in
client.stream and if the stream or client had to
buffer
the command in client.should_buffer. In combination this can be used to
implement backpressure by checking the buffer state before sending a command and
listening to the stream
drain event.

client.quit(callback)

This sends the quit command to the redis server and ends cleanly right after all
running commands were properly handled. If this is called while reconnecting
(and therefore no connection to the redis server exists) it is going to end the
connection right away instead of resulting in further reconnections! All offline
commands are going to be flushed with an error in that case.

client.end(flush)

Forcibly close the connection to the Redis server. Note that this does not wait
until all replies have been parsed. If you want to exit cleanly, call
client.quit() as mentioned above.

You should set flush to true, if you are not absolutely sure you do not care
about any other commands. If you set flush to false all still running commands
will silently fail.

This example closes the connection to the Redis server before the replies have
been read. You probably don't want to do this:

var redis = require("redis"),
    client = redis.createClient();

client.set("foo_rand000000000000", "some fantastic value", function (err, reply) {
    // This will either result in an error (flush parameter is set to true)
    // or will silently fail and this callback will not be called at all (flush set to false)
    console.log(err);
});
client.end(true); // No further commands will be processed
client.get("foo_rand000000000000", function (err, reply) {
    console.log(err); // => 'The connection has already been closed.'
});

client.end() without the flush parameter set to true should NOT be used in production!

Error handling (>= v.2.6)

Currently the following error subclasses exist:

• RedisError: All errors returned by the client
• ReplyError subclass of RedisError: All errors returned by Redis itself
• AbortError subclass of RedisError: All commands that could not finish due
  to what ever reason
• ParserError subclass of RedisError: Returned in case of a parser error
  (this should not happen)
• AggregateError subclass of AbortError: Emitted in case multiple unresolved
  commands without callback got rejected in debug_mode instead of lots of
  AbortErrors.

All error classes are exported by the module.

Example:

var redis = require('./');
var assert = require('assert');
var client = redis.createClient();

client.on('error', function (err) {
    assert(err instanceof Error);
    assert(err instanceof redis.AbortError);
    assert(err instanceof redis.AggregateError);
    // The set and get get aggregated in here
    assert.strictEqual(err.errors.length, 2);
    assert.strictEqual(err.code, 'NR_CLOSED');
});
client.set('foo', 123, 'bar', function (err, res) { // Too many arguments
    assert(err instanceof redis.ReplyError); // => true
    assert.strictEqual(err.command, 'SET');
    assert.deepStrictEqual(err.args, ['foo', 123, 'bar']);

    redis.debug_mode = true;
    client.set('foo', 'bar');
    client.get('foo');
    process.nextTick(function () {
        // Force closing the connection while the command did not yet return
        client.end(true);
        redis.debug_mode = false;
    });
});

Every ReplyError contains the command name in all-caps and the arguments (args).

If node_redis emits a library error because of another error, the triggering
error is added to the returned error as origin attribute.

Error codes

node_redis returns a NR_CLOSED error code if the clients connection dropped.
If a command unresolved command got rejected a UNCERTAIN_STATE code is
returned. A CONNECTION_BROKEN error code is used in case node_redis gives up
to reconnect.

client.unref()

Call unref() on the underlying socket connection to the Redis server, allowing
the program to exit once no more commands are pending.

This is an experimental feature, and only supports a subset of the Redis
protocol. Any commands where client state is saved on the Redis server, e.g.
*SUBSCRIBE or the blocking BL* commands will NOT work with .unref().

var redis = require("redis");
var client = redis.createClient();

/*
    Calling unref() will allow this program to exit immediately after the get
    command finishes. Otherwise the client would hang as long as the
    client-server connection is alive.
*/
client.unref();
client.get("foo", function (err, value) {
    if (err) throw(err);
    console.log(value);
});

Friendlier hash commands

Most Redis commands take a single String or an Array of Strings as arguments,
and replies are sent back as a single String or an Array of Strings. When
dealing with hash values, there are a couple of useful exceptions to this.

client.hgetall(hash, callback)

The reply from an HGETALL command will be converted into a JavaScript Object by
node_redis. That way you can interact with the responses using JavaScript
syntax.

Example:

client.hmset("hosts", "mjr", "1", "another", "23", "home", "1234");
client.hgetall("hosts", function (err, obj) {
    console.dir(obj);
});

Output:

{ mjr: '1', another: '23', home: '1234' }

client.hmset(hash, obj[, callback])

Multiple values in a hash can be set by supplying an object:

client.HMSET(key2, {
    "0123456789": "abcdefghij", // NOTE: key and value will be coerced to strings
    "some manner of key": "a type of value"
});

The properties and values of this Object will be set as keys and values in the
Redis hash.

client.hmset(hash, key1, val1, ... keyn, valn, [callback])

Multiple values may also be set by supplying a list:

client.HMSET(key1, "0123456789", "abcdefghij", "some manner of key", "a type of value");

Publish / Subscribe

Example of the publish / subscribe API. This program opens two
client connections, subscribes to a channel on one of them, and publishes to that
channel on the other:

var redis = require("redis");
var sub = redis.createClient(), pub = redis.createClient();
var msg_count = 0;

sub.on("subscribe", function (channel, count) {
    pub.publish("a nice channel", "I am sending a message.");
    pub.publish("a nice channel", "I am sending a second message.");
    pub.publish("a nice channel", "I am sending my last message.");
});

sub.on("message", function (channel, message) {
    console.log("sub channel " + channel + ": " + message);
    msg_count += 1;
    if (msg_count === 3) {
        sub.unsubscribe();
        sub.quit();
        pub.quit();
    }
});

sub.subscribe("a nice channel");

When a client issues a SUBSCRIBE or PSUBSCRIBE, that connection is put into
a "subscriber" mode. At that point, only commands that modify the subscription
set are valid and quit (and depending on the redis version ping as well). When
the subscription set is empty, the connection is put back into regular mode.

If you need to send regular commands to Redis while in subscriber mode, just
open another connection with a new client (hint: use client.duplicate()).

Subscriber Events

If a client has subscriptions active, it may emit these events:

"message" (channel, message)

Client will emit message for every message received that matches an active subscription.
Listeners are passed the channel name as channel and the message as message.

"pmessage" (pattern, channel, message)

Client will emit pmessage for every message received that matches an active
subscription pattern. Listeners are passed the original pattern used with
PSUBSCRIBE as pattern, the sending channel name as channel, and the
message as message.

"message_buffer" (channel, message)

This is the same as the message event with the exception, that it is always
going to emit a buffer. If you listen to the message event at the same time as
the message_buffer, it is always going to emit a string.

"pmessage_buffer" (pattern, channel, message)

This is the same as the pmessage event with the exception, that it is always
going to emit a buffer. If you listen to the pmessage event at the same time
as the pmessage_buffer, it is always going to emit a string.

"subscribe" (channel, count)

Client will emit subscribe in response to a SUBSCRIBE command. Listeners are
passed the channel name as channel and the new count of subscriptions for this
client as count.

"psubscribe" (pattern, count)

Client will emit psubscribe in response to a PSUBSCRIBE command. Listeners
are passed the original pattern as pattern, and the new count of subscriptions
for this client as count.

"unsubscribe" (channel, count)

Client will emit unsubscribe in response to a UNSUBSCRIBE command. Listeners
are passed the channel name as channel and the new count of subscriptions for
this client as count. When count is 0, this client has left subscriber mode
and no more subscriber events will be emitted.

"punsubscribe" (pattern, count)

Client will emit punsubscribe in response to a PUNSUBSCRIBE command.
Listeners are passed the channel name as channel and the new count of
subscriptions for this client as count. When count is 0, this client has
left subscriber mode and no more subscriber events will be emitted.

client.multi([commands])

MULTI commands are queued up until an EXEC is issued, and then all commands
are run atomically by Redis. The interface in node_redis is to return an
individual Multi object by calling client.multi(). If any command fails to
queue, all commands are rolled back and none is going to be executed (For
further information look at
transactions).

var redis  = require("./index"),
    client = redis.createClient(), set_size = 20;

client.sadd("bigset", "a member");
client.sadd("bigset", "another member");

while (set_size > 0) {
    client.sadd("bigset", "member " + set_size);
    set_size -= 1;
}

// multi chain with an individual callback
client.multi()
    .scard("bigset")
    .smembers("bigset")
    .keys("*", function (err, replies) {
        // NOTE: code in this callback is NOT atomic
        // this only happens after the the .exec call finishes.
        client.mget(replies, redis.print);
    })
    .dbsize()
    .exec(function (err, replies) {
        console.log("MULTI got " + replies.length + " replies");
        replies.forEach(function (reply, index) {
            console.log("Reply " + index + ": " + reply.toString());
        });
    });

Multi.exec([callback])

client.multi() is a constructor that returns a Multi object. Multi objects
share all of the same command methods as client objects do. Commands are
queued up inside the Multi object until Multi.exec() is invoked.

If your code contains an syntax error an EXECABORT error is going to be thrown
and all commands are going to be aborted. That error contains a .errors
property that contains the concrete errors.
If all commands were queued successfully and an error is thrown by redis while
processing the commands that error is going to be returned in the result array!
No other command is going to be aborted though than the onces failing.

You can either chain together MULTI commands as in the above example, or you
can queue individual commands while still sending regular client command as in
this example:

var redis  = require("redis"),
    client = redis.createClient(), multi;

// start a separate multi command queue
multi = client.multi();
multi.incr("incr thing", redis.print);
multi.incr("incr other thing", redis.print);

// runs immediately
client.mset("incr thing", 100, "incr other thing", 1, redis.print);

// drains multi queue and runs atomically
multi.exec(function (err, replies) {
    console.log(replies); // 101, 2
});

In addition to adding commands to the MULTI queue individually, you can also
pass an array of commands and arguments to the constructor:

var redis  = require("redis"),
    client = redis.createClient();

client.multi([
    ["mget", "multifoo", "multibar", redis.print],
    ["incr", "multifoo"],
    ["incr", "multibar"]
]).exec(function (err, replies) {
    console.log(replies);
});

Multi.exec_atomic([callback])

Identical to Multi.exec but with the difference that executing a single command
will not use transactions.

client.batch([commands])

Identical to .multi without transactions. This is recommended if you want to
execute many commands at once but don't have to rely on transactions.

BATCH commands are queued up until an EXEC is issued, and then all commands
are run atomically by Redis. The interface in node_redis is to return an
individual Batch object by calling client.batch(). The only difference
between .batch and .multi is that no transaction is going to be used.
Be aware that the errors are - just like in multi statements - in the result.
Otherwise both, errors and results could be returned at the same time.

If you fire many commands at once this is going to boost the execution speed
significantly compared to firing the same commands in a loop without waiting for
the result! See the benchmarks for further comparison. Please remember that all
commands are kept in memory until they are fired.

Optimistic Locks

Using multi you can make sure your modifications run as a transaction, but you
can't be sure you got there first. What if another client modified a key while
you were working with it's data?

To solve this, Redis supports the WATCH
command, which is meant to be used with MULTI:

var redis  = require("redis"),
    client = redis.createClient({ ... });

client.watch("foo", function( err ){
    if(err) throw err;

    client.get("foo", function(err, result) {
        if(err) throw err;
  
        // Process result
        // Heavy and time consuming operation here

        client.multi()
            .set("foo", "some heavy computation")
            .exec(function(err, results) {
                
                /**
                 * If err is null, it means Redis successfully attempted 
                 * the operation.
                 */ 
                if(err) throw err;
                
                /**
                 * If results === null, it means that a concurrent client
                 * changed the key while we were processing it and thus 
                 * the execution of the MULTI command was not performed.
                 * 
                 * NOTICE: Failing an execution of MULTI is not considered
                 * an error. So you will have err === null and results === null
                 */

            });
    });
});

The above snippet shows the correct usage of watch with multi. Every time a
watched key is changed before the execution of a multi command, the execution
will return null. On a normal situation, the execution will return an array of
values with the results of the operations.

As stated in the snippet, failing the execution of a multi command being watched
is not considered an error. The execution may return an error if, for example, the
client cannot connect to Redis.

An example where we can see the execution of a multi command fail is as follows:

let clients = {};
clients.watcher = redis.createClient({ ... } );
clients.alterer = clients.watcher.duplicate();

clients.watcher.watch('foo',function(err) {
  if (err) { throw err; }
  //if you comment out the next line, the transaction will work
  clients.alterer.set('foo',Math.random(), (err) => {if (err) { throw err; }})
  
  //using a setTimeout here to ensure that the MULTI/EXEC will come after the SET.
  //Normally, you would use a callback to ensure order, but I want the above SET command
  //to be easily comment-out-able.
  setTimeout(function() {
    clients.watcher
      .multi()
      .set('foo','abc')
      .set('bar','1234')
      .exec((err,results) => {
        if (err) { throw err; } 
        if (results === null) {
          console.log('transaction aborted because results were null');
        } else {
          console.log('transaction worked and returned',results)
        }
        clients.watcher.quit();
        clients.alterer.quit();
      });
  },1000);
});

WATCH limitations

Redis WATCH works only on whole key values. For example, with WATCH you can
watch a hash for modifications, but you cannot watch a specific field of a hash.

The following example would watch the keys foo and hello, not the field hello
of hash foo:

var redis  = require("redis"),
    client = redis.createClient({ ... });

client.hget( "foo", "hello", function(err, result){

    //Do some processing with the value from this field and watch it after
    
    client.watch("foo", "hello", function( err ){
        if(err) throw err;

         /**
         * WRONG: This is now watching the keys 'foo' and 'hello'. It is not
         * watching the field 'hello' of hash 'foo'. Because the key 'foo'
         * refers to a hash, this command is now watching the entire hash 
         * for modifications.  
         */ 
    });
} )

This limitation also applies to sets ( cannot watch individual set members )
and any other collections.

Monitor mode

Redis supports the MONITOR command, which lets you see all commands received
by the Redis server across all client connections, including from other client
libraries and other computers.

A monitor event is going to be emitted for every command fired from any client
connected to the server including the monitoring client itself. The callback for
the monitor event takes a timestamp from the Redis server, an array of command
arguments and the raw monitoring string.

Example:

var client  = require("redis").createClient();
client.monitor(function (err, res) {
    console.log("Entering monitoring mode.");
});
client.set('foo', 'bar');

client.on("monitor", function (time, args, raw_reply) {
    console.log(time + ": " + args); // 1458910076.446514:['set', 'foo', 'bar']
});

Extras

Some other things you might like to know about.

client.server_info

After the ready probe completes, the results from the INFO command are saved in
the client.server_info object.

The versions key contains an array of the elements of the version string for
easy comparison.

> client.server_info.redis_version
'2.3.0'
> client.server_info.versions
[ 2, 3, 0 ]

redis.print()

A handy callback function for displaying return values when testing. Example:

var redis = require("redis"),
    client = redis.createClient();

client.on("connect", function () {
    client.set("foo_rand000000000000", "some fantastic value", redis.print);
    client.get("foo_rand000000000000", redis.print);
});

This will print:

Reply: OK
Reply: some fantastic value

Note that this program will not exit cleanly because the client is still connected.

Multi-word commands

To execute redis multi-word commands like SCRIPT LOAD or CLIENT LIST pass
the second word as first parameter:

client.script('load', 'return 1');
client.multi().script('load', 'return 1').exec(...);
client.multi().exec(...);

client.duplicate([options][, callback])

Duplicate all current options and return a new redisClient instance. All options
passed to the duplicate function are going to replace the original option. If
you pass a callback, duplicate is going to wait until the client is ready and
returns it in the callback. If an error occurs in the meanwhile, that is going
to return an error instead in the callback.

One example of when to use duplicate() would be to accommodate the connection-
blocking redis commands BRPOP, BLPOP, and BRPOPLPUSH. If these commands
are used on the same redisClient instance as non-blocking commands, the
non-blocking ones may be queued up until after the blocking ones finish.

var Redis=require('redis');
var client = Redis.createClient();
var clientBlocking = client.duplicate();

var get = function() {
    console.log("get called");
    client.get("any_key",function() { console.log("get returned"); });
    setTimeout( get, 1000 );
};
var brpop = function() {
    console.log("brpop called");
    clientBlocking.brpop("nonexistent", 5, function() {
        console.log("brpop return");
        setTimeout( brpop, 1000 );
    });
};
get();
brpop();

Another reason to use duplicate() is when multiple DBs on the same server are
accessed via the redis SELECT command. Each DB could use its own connection.

client.send_command(command_name[, [args][, callback]])

All Redis commands have been added to the client object. However, if new
commands are introduced before this library is updated or if you want to add
individual commands you can use send_command() to send arbitrary commands to
Redis.

All commands are sent as multi-bulk commands. args can either be an Array of
arguments, or omitted / set to undefined.

redis.add_command(command_name)

Calling add_command will add a new command to the prototype. The exact command
name will be used when calling using this new command. Using arbitrary arguments
is possible as with any other command.

client.connected

Boolean tracking the state of the connection to the Redis server.

client.command_queue_length

The number of commands that have been sent to the Redis server but not yet
replied to. You can use this to enforce some kind of maximum queue depth for
commands while connected.

client.offline_queue_length

The number of commands that have been queued up for a future connection. You can
use this to enforce some kind of maximum queue depth for pre-connection
commands.

Commands with Optional and Keyword arguments

This applies to anything that uses an optional [WITHSCORES] or [LIMIT offset count] in the redis.io/commands documentation.

Example:

var args = [ 'myzset', 1, 'one', 2, 'two', 3, 'three', 99, 'ninety-nine' ];
client.zadd(args, function (err, response) {
    if (err) throw err;
    console.log('added '+response+' items.');

    // -Infinity and +Infinity also work
    var args1 = [ 'myzset', '+inf', '-inf' ];
    client.zrevrangebyscore(args1, function (err, response) {
        if (err) throw err;
        console.log('example1', response);
        // write your code here
    });

    var max = 3, min = 1, offset = 1, count = 2;
    var args2 = [ 'myzset', max, min, 'WITHSCORES', 'LIMIT', offset, count ];
    client.zrevrangebyscore(args2, function (err, response) {
        if (err) throw err;
        console.log('example2', response);
        // write your code here
    });
});

Performance

Much effort has been spent to make node_redis as fast as possible for common
operations.

Lenovo T450s, i7-5600U and 12gb memory
clients: 1, NodeJS: 6.2.0, Redis: 3.2.0, parser: javascript, connected by: tcp
         PING,         1/1 avg/max:   0.02/  5.26 2501ms total,   46916 ops/sec
         PING,  batch 50/1 avg/max:   0.06/  4.35 2501ms total,  755178 ops/sec
   SET 4B str,         1/1 avg/max:   0.02/  4.75 2501ms total,   40856 ops/sec
   SET 4B str,  batch 50/1 avg/max:   0.11/  1.51 2501ms total,  432727 ops/sec
   SET 4B buf,         1/1 avg/max:   0.05/  2.76 2501ms total,   20659 ops/sec
   SET 4B buf,  batch 50/1 avg/max:   0.25/  1.76 2501ms total,  194962 ops/sec
   GET 4B str,         1/1 avg/max:   0.02/  1.55 2501ms total,   45156 ops/sec
   GET 4B str,  batch 50/1 avg/max:   0.09/  3.15 2501ms total,  524110 ops/sec
   GET 4B buf,         1/1 avg/max:   0.02/  3.07 2501ms total,   44563 ops/sec
   GET 4B buf,  batch 50/1 avg/max:   0.10/  3.18 2501ms total,  473171 ops/sec
 SET 4KiB str,         1/1 avg/max:   0.03/  1.54 2501ms total,   32627 ops/sec
 SET 4KiB str,  batch 50/1 avg/max:   0.34/  1.89 2501ms total,  146861 ops/sec
 SET 4KiB buf,         1/1 avg/max:   0.05/  2.85 2501ms total,   20688 ops/sec
 SET 4KiB buf,  batch 50/1 avg/max:   0.36/  1.83 2501ms total,  138165 ops/sec
 GET 4KiB str,         1/1 avg/max:   0.02/  1.37 2501ms total,   39389 ops/sec
 GET 4KiB str,  batch 50/1 avg/max:   0.24/  1.81 2501ms total,  208157 ops/sec
 GET 4KiB buf,         1/1 avg/max:   0.02/  2.63 2501ms total,   39918 ops/sec
 GET 4KiB buf,  batch 50/1 avg/max:   0.31/  8.56 2501ms total,  161575 ops/sec
         INCR,         1/1 avg/max:   0.02/  4.69 2501ms total,   45685 ops/sec
         INCR,  batch 50/1 avg/max:   0.09/  3.06 2501ms total,  539964 ops/sec
        LPUSH,         1/1 avg/max:   0.02/  3.04 2501ms total,   41253 ops/sec
        LPUSH,  batch 50/1 avg/max:   0.12/  1.94 2501ms total,  425090 ops/sec
    LRANGE 10,         1/1 avg/max:   0.02/  2.28 2501ms total,   39850 ops/sec
    LRANGE 10,  batch 50/1 avg/max:   0.25/  1.85 2501ms total,  194302 ops/sec
   LRANGE 100,         1/1 avg/max:   0.05/  2.93 2501ms total,   21026 ops/sec
   LRANGE 100,  batch 50/1 avg/max:   1.52/  2.89 2501ms total,   32767 ops/sec
 SET 4MiB str,         1/1 avg/max:   5.16/ 15.55 2502ms total,     193 ops/sec
 SET 4MiB str,  batch 20/1 avg/max:  89.73/ 99.96 2513ms total,     223 ops/sec
 SET 4MiB buf,         1/1 avg/max:   2.23/  8.35 2501ms total,     446 ops/sec
 SET 4MiB buf,  batch 20/1 avg/max:  41.47/ 50.91 2530ms total,     482 ops/sec
 GET 4MiB str,         1/1 avg/max:   2.79/ 10.91 2502ms total,     358 ops/sec
 GET 4MiB str,  batch 20/1 avg/max: 101.61/118.11 2541ms total,     197 ops/sec
 GET 4MiB buf,         1/1 avg/max:   2.32/ 14.93 2502ms total,     430 ops/sec
 GET 4MiB buf,  batch 20/1 avg/max:  65.01/ 84.72 2536ms total,     308 ops/sec

Debugging

To get debug output run your node_redis application with NODE_DEBUG=redis.

This is also going to result in good stack traces opposed to useless ones
otherwise for any async operation.
If you only want to have good stack traces but not the debug output run your
application in development mode instead (NODE_ENV=development).

Good stack traces are only activated in development and debug mode as this
results in a significant performance penalty.

Comparison:
Useless stack trace:

ReplyError: ERR wrong number of arguments for 'set' command
    at parseError (/home/ruben/repos/redis/node_modules/redis-parser/lib/parser.js:158:12)
    at parseType (/home/ruben/repos/redis/node_modules/redis-parser/lib/parser.js:219:14)

Good stack trace:

ReplyError: ERR wrong number of arguments for 'set' command
    at new Command (/home/ruben/repos/redis/lib/command.js:9:902)
    at RedisClient.set (/home/ruben/repos/redis/lib/commands.js:9:3238)
    at Context.<anonymous> (/home/ruben/repos/redis/test/good_stacks.spec.js:20:20)
    at callFnAsync (/home/ruben/repos/redis/node_modules/mocha/lib/runnable.js:349:8)
    at Test.Runnable.run (/home/ruben/repos/redis/node_modules/mocha/lib/runnable.js:301:7)
    at Runner.runTest (/home/ruben/repos/redis/node_modules/mocha/lib/runner.js:422:10)
    at /home/ruben/repos/redis/node_modules/mocha/lib/runner.js:528:12
    at next (/home/ruben/repos/redis/node_modules/mocha/lib/runner.js:342:14)
    at /home/ruben/repos/redis/node_modules/mocha/lib/runner.js:352:7
    at next (/home/ruben/repos/redis/node_modules/mocha/lib/runner.js:284:14)
    at Immediate._onImmediate (/home/ruben/repos/redis/node_modules/mocha/lib/runner.js:320:5)
    at processImmediate [as _immediateCallback] (timers.js:383:17)

How to Contribute

• Open a pull request or an issue about what you want to implement / change. We're glad for any help!
• Please be aware that we'll only accept fully tested code.

Contributors

The original author of node_redis is Matthew Ranney

The current lead maintainer is Ruben Bridgewater

Many others
contributed to node_redis too. Thanks to all of them!

License

MIT

Consolidation: It's time for celebration

Right now there are two great redis clients around and both have some advantages
above each other. We speak about ioredis and node_redis. So after talking to
each other about how we could improve in working together we (that is @luin and
@BridgeAR) decided to work towards a single library on the long run. But step by
step.

First of all, we want to split small parts of our libraries into others so that
we're both able to use the same code. Those libraries are going to be maintained
under the NodeRedis organization. This is going to reduce the maintenance
overhead, allows others to use the very same code, if they need it and it's way
easyer for others to contribute to both libraries.

We're very happy about this step towards working together as we both want to
give you the best redis experience possible.

If you want to join our cause by help maintaining something, please don't
hesitate to contact either one of us.