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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-19 00:47:55 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-19 00:47:55 +0000 |
commit | 26a029d407be480d791972afb5975cf62c9360a6 (patch) | |
tree | f435a8308119effd964b339f76abb83a57c29483 /docs/code-quality/coding-style/coding_style_js.rst | |
parent | Initial commit. (diff) | |
download | firefox-26a029d407be480d791972afb5975cf62c9360a6.tar.xz firefox-26a029d407be480d791972afb5975cf62c9360a6.zip |
Adding upstream version 124.0.1.upstream/124.0.1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | docs/code-quality/coding-style/coding_style_js.rst | 147 |
1 files changed, 147 insertions, 0 deletions
diff --git a/docs/code-quality/coding-style/coding_style_js.rst b/docs/code-quality/coding-style/coding_style_js.rst new file mode 100644 index 0000000000..09d7a6fc8a --- /dev/null +++ b/docs/code-quality/coding-style/coding_style_js.rst @@ -0,0 +1,147 @@ +======================= +JavaScript Coding style +======================= + +Coding style +~~~~~~~~~~~~ + +`prettier <https://prettier.io/>`_ is the tool used to reformat the JavaScript code. + + +Methods and functions +~~~~~~~~~~~~~~~~~~~~~ + +In JavaScript, functions should use camelCase, but should not capitalize +the first letter. Methods should not use the named function expression +syntax, because our tools understand method names: + +.. code-block:: cpp + + doSomething: function (aFoo, aBar) { + ... + } + +In-line functions should have spaces around braces, except before commas +or semicolons: + +.. code-block:: cpp + + function valueObject(aValue) { return { value: aValue }; } + + +JavaScript objects +~~~~~~~~~~~~~~~~~~ + +.. code-block:: cpp + + var foo = { prop1: "value1" }; + + var bar = { + prop1: "value1", + prop2: "value2" + }; + +Constructors for objects should be capitalized and use Pascal Case: + +.. code-block:: cpp + + function ObjectConstructor() { + this.foo = "bar"; + } + + +Operators +~~~~~~~~~ + +In JavaScript, overlong expressions not joined by ``&&`` and +``||`` should break so the operator starts on the second line and +starting in the same column as the beginning of the expression in the +first line. This applies to ``?:``, binary arithmetic operators +including ``+``, and member-of operators. Rationale: an operator at the +front of the continuation line makes for faster visual scanning, as +there is no need to read to the end of line. Also there exists a +context-sensitive keyword hazard in JavaScript; see {{bug(442099, "bug", +19)}}, which can be avoided by putting . at the start of a continuation +line, in long member expression. + +In JavaScript, ``==`` is preferred to ``===``. + +Unary keyword operators, such as ``typeof``, should have their operand +parenthesized; e.g. ``typeof("foo") == "string"``. + +Literals +~~~~~~~~ + +Double-quoted strings (e.g. ``"foo"``) are preferred to single-quoted +strings (e.g. ``'foo'``), in JavaScript, except to avoid escaping +embedded double quotes, or when assigning inline event handlers. + + +Prefixes +~~~~~~~~ + +- k=constant (e.g. ``kNC_child``). Not all code uses this style; some + uses ``ALL_CAPS`` for constants. +- g=global (e.g. ``gPrefService``) +- a=argument (e.g. ``aCount``) + +- JavaScript Specific Prefixes + + - \_=member (variable or function) (e.g. ``_length`` or + ``_setType(aType)``) + - k=enumeration value (e.g. ``const kDisplayModeNormal = 0``) + - on=event handler (e.g. ``function onLoad()``) + - Convenience constants for interface names should be prefixed with + ``nsI``: + + .. code-block:: javascript + + const nsISupports = Components.interfaces.nsISupports; + const nsIWBN = Components.interfaces.nsIWebBrowserNavigation; + + + +Other advices +~~~~~~~~~~~~~ + +- Do not compare ``x == true`` or ``x == false``. Use ``(x)`` or + ``(!x)`` instead. ``x == true``, is certainly different from if + ``(x)``! Compare objects to ``null``, numbers to ``0`` or strings to + ``""``, if there is chance for confusion. +- Make sure that your code doesn't generate any strict JavaScript + warnings, such as: + + - Duplicate variable declaration. + - Mixing ``return;`` with ``return value;`` + - Undeclared variables or members. If you are unsure if an array + value exists, compare the index to the array's length. If you are + unsure if an object member exists, use ``"name"`` in ``aObject``, + or if you are expecting a particular type you may use + ``typeof(aObject.name) == "function"`` (or whichever type you are + expecting). + +- Use ``['value1, value2']`` to create a JavaScript array in preference + to using + ``new {{JSxRef("Array", "Array", "Syntax", 1)}}(value1, value2)`` + which can be confusing, as ``new Array(length)`` will actually create + a physically empty array with the given logical length, while + ``[value]`` will always create a 1-element array. You cannot actually + guarantee to be able to preallocate memory for an array. +- Use ``{ member: value, ... }`` to create a JavaScript object; a + useful advantage over ``new {{JSxRef("Object", "Object", "", 1)}}()`` + is the ability to create initial properties and use extended + JavaScript syntax, to define getters and setters. +- If having defined a constructor you need to assign default + properties, it is preferred to assign an object literal to the + prototype property. +- Use regular expressions, but use wisely. For instance, to check that + ``aString`` is not completely whitespace use + ``/\S/.{{JSxRef("RegExp.test", "test(aString)", "", 1)}}``. Only use + {{JSxRef("String.search", "aString.search()")}} if you need to know + the position of the result, or {{JSxRef("String.match", + "aString.match()")}} if you need to collect matching substrings + (delimited by parentheses in the regular expression). Regular + expressions are less useful if the match is unknown in advance, or to + extract substrings in known positions in the string. For instance, + {{JSxRef("String.slice", "aString.slice(-1)")}} returns the last + letter in ``aString``, or the empty string if ``aString`` is empty. |