In MongoDB 2.4, :dbcommand:`map-reduce operations <mapReduce>`, the :dbcommand:`group` command, and :query:`$where` operator expressions cannot access certain global functions or properties, such as db, that are available in the :program:`mongo` shell.

When upgrading to MongoDB 2.4, you will need to refactor your code if your :dbcommand:`map-reduce operations <mapReduce>`, :dbcommand:`group` commands, or :query:`$where` operator expressions include any global shell functions or properties that are no longer available, such as db.

The following JavaScript functions and properties are available to :dbcommand:`map-reduce operations <mapReduce>`, the :dbcommand:`group` command, and :query:`$where` operator expressions in MongoDB 2.4:

Available Properties	Available Functions
`args` `MaxKey` `MinKey`	`assert()` `BinData()` `DBPointer()` `DBRef()` `doassert()` `emit()` `gc()` `HexData()` `hex_md5()` `isNumber()` `isObject()` `ISODate()` `isString()`	`Map()` `MD5()` `NumberInt()` `NumberLong()` `ObjectId()` `print()` `printjson()` `printjsononeline()` `sleep()` `Timestamp()` `tojson()` `tojsononeline()` `tojsonObject()` `UUID()` `version()`

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