Javascript/Coding Style

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The Moodle JavaScript coding style

Overview

Although most of the Moodle standard Coding style applies to JavaScript, there are a number of exceptions. These are largely as a result of common practice within the JavaScript community, or for increased clarity given different terminology when dealing with frontend code (e.g. use of cartesian positions).

Scope

This document describes style guidelines for developers work on or with JavaScript code in Moodle.

Goals

Consistent coding style is important in any development project, and particularly when many developers are involved. A standard style helps to ensure that the code is easier to read and understand, which helps overall quality.

Abstract goals we strive for:

  • simplicity
  • readability
  • tool friendliness

Naming conventions

Variable and function naming

Contrary to the standard Moodle coding style, we prefer to use camelCase for JavaScript.

The justification for this is that:

  • it is a commonly accepted practice within the wider JavaScript community;
  • it is easier to read when dealing with variables describing cartesian points which are more common in JavaScript than PHP (e.g. currenty versus currentY); and
  • it is the style used by the upstream YUI library for all variable names, and all CSS settings (keeping consistency within the codebase).

Correct

var currentY,
    courseCategory,
    lastValue,
    lastBackgroundColor;
 
function doSomething() {
}
 
function doSomethingElse() {
}

Incorrect

var current_y,
    currenty,
    course_category,
    coursecategory,
    last_value,
    lastvalue,
    last_background_color,
    lastbackgroundcolor;
 
function dosomething() {
}
 
function do_something_else() {
}

Class naming

In line with common JavaScript practices, names of new classes being defined should be written using CamelCase starting with an uppercase letter.

This helps to clearly separate variables, and standard functions from those used to create a new instance.

Correct

// The instantiator:
function Pantry() {
    // Setup code goes here.
}
 
// Making use of it:
var myPantry = new Pantry();
 
 
// And another:
function PantryShelf() {
}
 
var myPantryShelf = new PantryShelf();

Incorrect

// There is no distinction here between a normal function, and one used to
// create a new object:
function pantry() {
}
 
// This results in an unclear object creation:
var myPantry = new pantry();
 
// This one is also incorrect, despite using camelCase:
function pantryShelf() {
}
var myPantryShelf = new pantryShelf();
 
// This one is also incorrect:
function pantry_shelf() {
}
var myPantryShelf = new pantry_shelf();

Variable declaration

As usual with JavaScript, all variables must:

  • be declared before they are used and using the var keyword;
  • be declared once, and only once, for the scope in which they are used;
  • only be declared if they are to be used; and
  • use sensible naming, following the naming convention.

Number of variable declarations

The number of variable declarations should be kept to a sensible minimum, though this interpretation is left largely up to the individual developer.

Where a set of variables is separated by block of code, it is reasonable to logically separate the sets of variables around the code block.

Correct

var oneVariable,
    twoVariable,
    threeVariable,
    more;
 
// Some other code goes here which breaks up the logical flow
oneVariable = Y.Node.Create('<div></div>');
twoVariable = Y.one('#someid');
 
// Some more variable definitions relating to the next set of code goes
// here.
var anotherVariable,
    andAnother;

Incorrect

// Only one variable definition should be used:
var oneVariable;
var twoVariable;
var threeVariable;
var more;

Initial values

Variable definitions describing variables which have initial content should:

  • fit on a single line in the case of simple types; and
  • be spread across multiple lines for complex types (including all
 objects and arrays, no matter how simple) - this includes those which are
 empty.

The reason for this is primarily to help preserve revision and change history for different lines of code in a sensible and meaningful fashion.

Correct

var someBoolean = true,
    someNumber = 10,
    anObjectWithoutContent = {
    },
    anObjectWithContent = {
        exampleContent: 'value'
    };

Incorrect

var anObjectWithContent = {},
    anObjectWithContent = {exampleContent: 'value')};

Function definition

Function definitions must meet the following rules:

  • they must be documented using standard YUIDoc tags; and
  • they must not declare variables which they do not intend to use within
 the function body;
    • unless the argument is before an actively used argument in the function
  declaration;
  • variables defined in the function declaration must not be re-declared
 within the function.

Correct

/**
 * Do something with the two values provided and return something else.
 *
 * @method doSomething
 * @param optionOne {Number} The first parameter
 * @param unusedMiddleArgument {Number} This parameter is not used in this
 * function definition, but perhaps it's provided by the event calling it
 * so we have to have it and cannot remove it.
 * @param optionTwo {Number} The second parameter
 * @return Number The result of a really complex mathematical equation
 * which you couldn't possible do your own
 */
var doSomething = function(optionOne, unusedMiddleArgument, optionTwo) {
    return optionOne + optionTwo;
};

Incorrect

// Undocumented function:
var doSomething = function(anArgument, anotherArgument, aThirdArgument) {
    // The second argument is re-declared:
    var anotherArgument = anArgument + 1;
 
    // The third argument is never used:
    return anArgument + anotherArgument;
};

Line length

The key thing here is readability. Aim for shorter lines broken up naturally, and with a maximum length of 150 characters.

Line wrapping

Statement wrapping

When wrapping a long line as part of a statement, indent the following line by 8 spaces rather than 4. For example:

if (someObject.hasClass(CSS.CLASSTOTEST) &&
        someOtherObject.hasClass(CSS.CLASSTOTEST)) {
    return true;
}

Method call wrapping

When wrapping a long line which consists of a chained series of functions, break the line at the end of each function, and continue the next chain on a new line.

The line should be indented by 4 spaces.

The start of each line should contain the concatanation character, and the final line should contain a trailing semicolon.

Correct
var childNode = Y.Node.create('<div />')
    .addClass(CSS.SOMECLASS)
    .setAttribute('someAttribute', 'someValue')
    .appendTo(parentNode);
Incorrect
// All on one line:
var childNode = Y.Node.create('<div />').addClass(CSS.SOMECLASS).setAttribute('someAttribute', 'someValue').appendTo(parentNode);
 
// A mix of separation and line concatanation:
var childNode = Y.Node.create('<div />').addClass(CSS.SOMECLASS)
    .setAttribute('someAttribute', 'someValue').appendTo(parentNode);
 
// The concatanation character is at the end of the line:
var childNode = Y.Node.create('<div />').
    addClass(CSS.SOMECLASS).
    setAttribute('someAttribute', 'someValue').
    appendTo(parentNode);

Whitespace

Operators

There should be a space around all operators to help improve legibility of code. This includes:

  • =
  • &&
  • ||
  • ===

Correct

var a = 1,
    b = (a && 1),
    c = (b || 1),
    d = (b === c);

Incorrect

var a=1,
    b= (a&&1),
    c =(b||1),
    d = (b===c);

Assignation

In the case of object property assignation, there should be a space after the colon, but not before.

Correct

var anObject = {
    someKey: 'someValue',
    anotherKey: Y.one(SELECTORS.FOO)
};


Incorrect

var anObject = {
    // Incorrect because a space is present both before and after the assignation character:
    someKey : 'someValue',
 
    // Incorrect because there is no whitespace either side of the assignation character:
    anotherKey:Y.one(SELECTORS.FOO)
};

Documentation and comments

We are attempting to document all YUI modules that we write and as such largely follow the upstream YUI guidance which is available at http://yui.github.io/yuidoc/syntax/index.html.

General notes

  • Unless otherwise specified, comments should conform to the general style guidelines;
  • all comments must start with leading whitespace before the first word on each line; and
  • all indentation must be in addition to any existing leading whitespace on the line.

Official documentation

All JavaScript documentation must:

  • use the correct docblock format;
  • use the correct JavaScript types where relevant (note, Int is not a valid type in JavaScript);
  • use all appropriate tags;
  • produce valid documentation using the YUIDoc toolset;
  • have a linebreak between the description and the list of tags.

Note:

YUIDoc will only generate documentation for docblocks starting with /**.

YUIDoc will try to generate documentation for *all* docblocks starting /**.

Correct

/**
 * This is an example docblock comment. It describes a function called
 * marmite.
 *
 * It adds a number of jars of marmite to the cupboard.
 *
 * @method addMarmite
 * @param {Number} [jarCount=1] The number of jars of marmite to add to the
 * cupboard. This parameter is optional and defaults to 1.
 * @chainable
 */

Incorrect

/*
 * This is an invalid comment block. It wouldn't be picked up by yuidoc as
 * the comment style is incorrect.
 *
 * @method foo
 */
 
// This is also an invalid comment block and wouldn't be picked up by
// YUIDoc.
 
/**
* Although this style would be picked up by YUIDoc, it is hard to read.
*
* @method foo
*/
 
/**
 *Although this style would be picked up by YUIDoc, it is also hard to read.
 *
 *@method foo
 */
 
/**
 * This docblock is mostly valid but does not include a linebreak between
 * the description, and the tags.
 * @method foo
 */


General comments

All shorter comments, for example those explaining the subsequent few lines of code should use the // style of comments.

Comments not intended for official documentation must *not* use the Docblock style of commenting as YUIDoc will attempt to include the comment in official documentation.

Correct

// This is a valid set of comments for one line.
 
// And this is a valid longer comment to describe the subsequent few lines
// in as much detail as required. It can consist of multiple sentences, as
// long as each new line starts with the correct comment style.

Incorrect

/* This is an invalid comment style for short comments. */
 
//This is also an invalid style as there is no leading whitespace after the
//comment indicator.
 
/**
 * This is an invalid multi-line comment. Multi-line comments should not
 * use the docblock style comments unless they are a valid and fully
 * formatted docblock.
 */
 
/*
 * This is an also invalid multi-line comment. Although it is not a full
 * docblock style, it does not start with the // style of comment
 * indicator.
 */

See Also