Server-side JavaScript
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Overview
MongoDB provides the following commands, methods, and operator that perform server-side execution of JavaScript code:
mapReduceand the correspondingmongoshmethoddb.collection.mapReduce(). For more information, see Map-Reduce.$whereoperator that evaluates a JavaScript expression or a function in order to query for documents.$accumulatorand$functionaggregation 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 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
mongodinstance by passing the--noscriptingoption on the command line or settingsecurity.javascriptEnabledto false in the configuration file.For a
mongosinstance by passing the--noscriptingoption on the command line or settingsecurity.javascriptEnabledto false in the configuration file.
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.