Server-side JavaScript¶

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Overview
Running .js files via a mongosh Instance on the Server
Disable Server-Side Execution of JavaScript
Behavior

Overview¶

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

mapReduce and the corresponding mongosh method db.collection.mapReduce(). For more information, see Map-Reduce.
$where operator that evaluates a JavaScript expression or a function in order to query for documents.
$accumulator and $function aggregation operations that allows users to define custom aggregation expressions.

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

Note

JavaScript in MongoDB

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

If you do not need to perform server-side execution of JavaScript code, 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 `mongosh` Instance on the Server¶

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

Disable Server-Side Execution of JavaScript¶

You can disable all server-side execution of JavaScript:

For a mongod instance by passing the --noscripting option on the command line or setting security.javascriptEnabled to false in the configuration file.
Starting in MongoDB 4.4, for a mongos instance by passing the --noscripting option on the command line or setting security.javascriptEnabled to false in the configuration file.

In earlier versions, MongoDB does not allow JavaScript execution on mongos instances.

Behavior¶

Concurrency¶

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

Unsupported Array and String Functions¶

MongoDB 6.0 upgrades the internal JavaScript engine used for server-side JavaScript, $accumulator, $function, and $where expressions and from MozJS-60 to MozJS-91. Several deprecated, non-standard array and string functions that existed in MozJS-60 are removed in MozJS-91.

For the complete list of removed array and string functions, see the 6.0 compatibility notes.