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## Concurrency 

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 (page 759). 

## 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. 

## See also: 

Store a JavaScript Function on the Server (page 235) 

## Data Types in the mongo Shell 

MongoDB BSON provides support for additional data types than JSON . Drivers provide native support for these data types in host languages and the mongo shell also provides several helper classes to support the use of these data types in the mongo JavaScript shell. See the Extended JSON reference for additional information. 

