DOCS-6615: Document 3.2 JavaScript changes

config/redirects.yaml

@@ -874,6 +874,13 @@ code: 303
 outputs:
  - 'before-v3.0'
 ---
+from: '/release-notes/3.2-javascript'
+to: '/release-notes'
+type: 'redirect'
+code: 303
+outputs:
+ - 'before-v3.0'
+---
 from : '/core/index-partial'
 to: '/core/index-sparse'
 type: 'redirect'

source/includes/options-mongo.yaml

@@ -332,4 +332,14 @@ inherit:
   name: sslAllowInvalidHostnames
   program: _shared
   file: options-shared.yaml
+---
+program: mongo
+name: disableJavaScriptJIT
+directive: option
+optional: true
+args: null
+description: |
+   .. versionadded:: 3.2
+
+   Disables use of the JavaScript engine's JIT compiler.
 ...

source/reference/command/buildInfo.txt

@@ -85,11 +85,11 @@ These fields are stable and should provide consistent behavior.
 
 .. data:: buildInfo.javascriptEngine
 
-   .. versionchanged:: 2.4
+   .. versionchanged:: 3.2
 
    A string that reports the JavaScript engine used in the
-   :program:`mongod` instance. By default, this is ``V8`` after
-   version 2.4, and ``SpiderMonkey`` before 2.4.
+   :program:`mongod` instance. By default, this is ``mozjs`` after
+   version 3.2, and previously ``V8``.
 
 .. data:: buildInfo.bits
 

source/reference/command/setParameter.txt

@@ -53,5 +53,9 @@ setParameter
    - :parameter:`syncdelay`
    - :parameter:`wiredTigerEngineRuntimeConfigSetting`
 
+   **JavaScript**
+
+   - :parameter:`disableJavaScriptJIT`
+
    .. slave-ok, admin-only
    .. textSearchEnabled, deprecated v2.6

source/reference/parameters.txt

@@ -376,7 +376,7 @@ General Parameters
       db.getSiblingDB('admin').runCommand( { setParameter: 1, failIndexKeyTooLong: false } )
 
    You can also set :parameter:`failIndexKeyTooLong`  at
-   run-time with the following operation.
+   startup time with the following option:
 
    .. code-block:: sh
 
@@ -462,13 +462,42 @@ General Parameters
 
       db.getSiblingDB('admin').runCommand( { setParameter: 1, ttlMonitorEnabled: false } )
 
-   Alternately, you may disable the thread at run-time by starting the
+   Alternately, you may disable the thread at startup time by starting the
    :program:`mongod` instance with the following option:
 
    .. code-block:: sh
 
       mongod --setParameter ttlMonitorEnabled=false
 
+
+.. parameter:: disableJavaScriptJIT
+
+   .. versionadded:: 3.2
+
+   |mongod-only|
+
+   The MongoDB JavaScript engine uses SpiderMonkey, which implements
+   Just-in-Time (JIT) compilation for improved performance when running scripts.
+
+   To disable the JIT, set :parameter:`disableJavaScriptJIT` to ``true``, as in
+   the following example:
+
+   .. code-block:: javascript
+
+      db.getSiblingDB('admin').runCommand( { setParameter: 1, disableJavaScriptJIT: true } )
+
+   Be aware that :dbcommand:`group` and :query:`$where` will reuse existing
+   JavaScript interpreter contexts, so changes to
+   :parameter:`disableJavaScriptJIT` may not take effect immediately for these
+   operations.
+
+   Alternately, you may disable the JIT at startup time by starting the
+   :program:`mongod` instance with the following option:
+
+   .. code-block:: sh
+
+      mongod --setParameter disableJavaScriptJIT=true
+
 Logging Parameters
 ~~~~~~~~~~~~~~~~~~
 
@@ -585,7 +614,7 @@ Logging Parameters
       } )
 
    You can also set parameter :parameter:`logComponentVerbosity` at
-   run-time, passing the verbosity level document as a string.
+   startup time, passing the verbosity level document as a string.
 
    :program:`mongo` shell also provides the :method:`db.setLogLevel()`
    to set the log level for a single component. For various ways to set
@@ -653,7 +682,7 @@ To support the :ref:`diagnostic data capture
 <3.2-diagnostic-data-capture>`, MongoDB introduces the following
 parameters:
 
-.. note:: 
+.. note::
 
    The default values for the diagnostic data capture interval and the
    maximum sizes are chosen to provide useful data to MongoDB engineers
@@ -903,7 +932,7 @@ WiredTiger Parameters
 
    .. code-block:: javascript
 
-      db.adminCommand({ 
+      db.adminCommand({
          "setParameter": 1,
          "wiredTigerEngineRuntimeConfig": "<option>=<setting>,<option>=<setting>"
       })

source/reference/program/mongo.txt

@@ -65,6 +65,8 @@ Core Options
 
 .. include:: /includes/option/option-mongo-<db address>.rst
 
+.. include:: /includes/option/option-mongo-disableJavaScriptJIT.rst
+
 .. _mongo-shell-file:
 
 .. include:: /includes/option/option-mongo-<file.js>.rst

source/release-notes/3.2-compatibility.txt

@@ -130,8 +130,18 @@ Aggregation Compatibility Changes
 SpiderMonkey Compatibility Changes
 ----------------------------------
 
-The change to SpiderMonkey may cause incompatibility issues for
-JavaScript code that relies on specific V8 functionality/behavior.
+.. class:: hidden
+
+   .. toctree::
+
+      /release-notes/3.2-javascript
+
+MongoDB 3.2 changes the JavaScript engine from V8 to SpiderMonkey. The change
+allows the use of more modern JavaScript language features, and comes along with
+minor :program:`mongo` shell improvements and compatibility changes.
+
+See :doc:`/release-notes/3.2-javascript` for more information about
+this change.
 
 .. _3.2-driver-compatibility:
 

source/release-notes/3.2-javascript.txt

@@ -0,0 +1,56 @@
+=================================
+JavaScript Changes in MongoDB 3.2
+=================================
+
+.. default-domain:: mongodb
+
+In MongoDB 3.2, the javascript engine used for both the :program:`mongo` shell
+and for server-side javascript in :program:`mongod` changed from V8 to
+`SpiderMonkey <https://developer.mozilla.org/en-US/docs/SpiderMonkey>`_.
+
+To confirm which JavaScript engine you are using, you can use either
+:js:func:`interpreterVersion()` method in the :program:`mongo` shell and the
+:data:`~buildInfo.javascriptEngine` field in the output of
+:method:`db.serverBuildInfo()`
+
+In MongoDB 3.2, this will appear as ``MozJS-38`` and ``mozjs``, respectively.
+
+Modernized JavaScript Implementation (ES6)
+------------------------------------------
+
+SpiderMonkey brings with it increased support for features defined in the 6th
+edition of `ECMAScript
+<http://www.ecma-international.org/ecma-262/6.0/index.html>`_,
+abbreviated as ES6. ES6 adds many new language features, including:
+
+- `arrow functions
+  <http://www.ecma-international.org/ecma-262/6.0/index.html#sec-arrow-function-definitions>`_,
+
+- `destructuring assignment
+  <http://www.ecma-international.org/ecma-262/6.0/index.html#sec-destructuring-assignment>`_,
+
+- `for-of loops
+  <http://www.ecma-international.org/ecma-262/6.0/index.html#sec-for-in-and-for-of-statements>`_, and
+
+- `generators
+  <http://www.ecma-international.org/ecma-262/6.0/index.html#sec-generator-function-definitions>`_.
+
+Changes to the ``mongo`` Shell
+------------------------------
+
+MongoDB 3.2 will return JavaScript and BSON
+:bsontype:`undefined <data_undefined>` values intact if saved into a collection.
+Previously, the :program:`mongo` shell would convert ``undefined`` values into
+``null``.
+
+MongoDB 3.2 also adds the :parameter:`disableJavaScriptJIT` parameter to
+:program:`mongod`, which allows you to disable the JavaScript engine's JIT
+acceleration. The :program:`mongo` shell has a corresponding
+:option:`--disableJavaScriptJIT` flag.
+
+Removed Non-Standard V8 Features
+--------------------------------
+
+SpiderMonkey does **not** allow the non-standard ``Error.captureStackTrace()``
+function that prior versions of MongoDB supported. If you must record stack
+traces, you can capture the ``Error().stack`` property as a workaround.