Server-side 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.

Note

If you are using SELinux, any MongoDB operation that requires server-side JavaScript will result in segfault errors. Disable Server-Side Execution of JavaScript describes how to disable execution of server-side 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.

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.