Server-side JavaScript¶

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Overview
Running .js files via a mongo shell Instance on the Server
Concurrency
Disable Server-Side Execution of JavaScript

Overview¶

MongoDB provides the following commands, methods, and operator that perform server-side execution of JavaScript code:

mapReduce and the corresponding mongo shell method db.collection.mapReduce(). mapReduce operations map, or associate, values to keys, and for keys with multiple values, reduce the values for each key to a single object. For more information, see Map-Reduce.
$where operator that evaluates a JavaScript expression or a function in order to query for documents.

You can also specify a JavaScript file to the mongo shell to run on the server. For more information, see Running .js files via a mongo shell Instance on the Server

JavaScript in MongoDB

Although these methods use JavaScript, most interactions with MongoDB do not use JavaScript but use an idiomatic driver in the language of the interacting application.

You can also disable server-side execution of JavaScript. For details, see Disable Server-Side Execution of JavaScript.

Running `.js` files via a `mongo` shell Instance on the Server¶

You can specify a JavaScript (.js) file to a mongo shell instance to execute the file on the server. This is a good technique for performing batch administrative work. When you run mongo shell on the server, connecting via the localhost interface, the connection is fast with low latency.

For more information, see Write Scripts for the mongo Shell.

Concurrency¶

Changed in version 3.2: MongoDB 3.2 uses SpiderMonkey as the JavaScript engine for the mongo shell. For information on this change, see JavaScript Changes in MongoDB 3.2.

Changed in version 2.4: The V8 JavaScript engine, which became the default in 2.4, allows multiple JavaScript operations to execute at the same time. Prior to 2.4, MongoDB operations that required the JavaScript interpreter had to acquire a lock, and a single mongod could only run a single JavaScript operation at a time.

Refer to the individual method or operator documentation for any concurrency information. See also the concurrency table.

Disable Server-Side Execution of JavaScript¶

You can disable all server-side execution of JavaScript, by passing the --noscripting option on the command line or setting security.javascriptEnabled in a configuration file.