1.6. JavaScript

1.6.1. General

  • Variable declarations must start with ‘var’.

  • Try your best to never to use a semicolon. This means avoiding them at line breaks and avoiding multi-statement lines. A semi-colon at the end of the line is only added when required.

  • Use 4 space indentation.

  • Use variables, functions, methods and constants names following PEP8. variable_name, function_name, methodName, ClassName, CONSTANT_NAME

  • Callback methods should always end with ‘Callback’ as the method / function name. This is a reminder of the fact that the context is lost.

  • Constructor functions (those that are called with new) should use class naming convention.

  • use === instead of == for comparison. === doesn’t do type coercion.

  • Only use typeof for checking against undefined variables:

    typeof foo !== 'undefined'
    
  • For all other type checking use the custom defined typeOf() function.

  • Try to avoid the usage of instanceof and don’t use it for native types.

  • Create new arrays using the array literals [] notation. Don’t use new Array().

  • Iterate through arrays using the classic for loop:

    var list = [1, 2, 3, 4, 5, ...... 100000000];
    for (var i = 0, l = list.length; i == l; i++) {
        console.log(list[i]);
    }
    
  • Always define the variable used to iterate into the for loop first statement.

  • Don’t use eval and don’t pass strings to setTimeout and setInterval.

  • Use undefined instead of the the traditional null.

  • Keep braces on the same line as their corresponding statements. Never omit them for single-line if / else statements.

if (something) {
    // code here
} else {
    // code here
}

function duppy() {
    var something
    return {
        foo: function() {}
    }
}
  • Leave 2 empty lines between global function or class definitions. Leave 1 empty line between functions from the same class. Global variables can be grouped and the don’t require empty lines in between them.
var GLOBAL_DAY = 1
var GLOBAL_YEAR = 3


/*
Docstring for duppy.
*/
function duppy() {
    // Do something here.
}


/*
Docstring for duppy_doo.
*/
function duppy_doo() {
    // Do something here.
}


/*
A simple mock for Browser service.
*/
function MockBrowser() {
    this._cookies = {}

    /*
    Docstring for MockBrower.setCookies()
    */
    this.setCookie = function(name, value) {
        // Implementation here.
    }

    /*
    Docstring here.
    */
    this.doSomethingElse = function(name) {
        // Implementation here.
    }

    this._methodWihoutDocstring = function(name) {
        // Implementation here.
    }

}
  • Avoid using leading parenthesis.
  • Avoid using the delete operator and only use it to delete explicitly set properties on normal objects:
var obj = {x: 1};
obj.y = 2;
delete obj.x;  // true
delete obj.y;  // true
  • Use single quote for strings.

Example:

In HTML, we use " as quotes around attribute values, like this:
<a href="foo">bar</a>
In JavaScript, we use ' as much as possible.

alert('qux');
This way, we can use consistent quotes when writing HTML inside of JS:

alert('<a href="foo">bar</a>')
  • REST web services should always return a valid dictionary and not an Array or a primitive. JSON-RPC is forced to return a dictionary by the protocol.
  • Callbacks called from the GUI / DOM should be prefixed with on. Ex: onAuthentication (when authenticate button is pressed), onLogout (when logout link is pressed), onLoginFormSubmit (when login form is submitted)
  • Callbacks/Errback for XHR are be prefixed with cb and eb, similar with Python/Twisted convention.
  • For one line comments, leave one empty space after the comment marker.
// Good comment line.
//Bad comment line.
  • For multi line comments use the following convention.
/*
Short single line comment title.
More details about what is here and
here and here.

Feel free to create paragraphs separation.
*/
  • Global constants will follow the CONSTANT_NAME naming convention.
  • Global services (objects with methods) are named similar to class names. Most of the time they will be singletons so there will be no associated class.
var Shell = new ActiveXObject("WScript.Shell");

function do_something() {
    var bla = Shell.method_usage()
}

TODO http://javascript.crockford.com/code.html http://jibbering.com/faq/notes/code-guidelines/ http://neil.rashbrook.org/Js.htm

1.6.2. Prevent polluting the global scope

You can use immediately invoked function expression IIFE to avoid injecting more variables into global scope. When using IIFE don’t forget to add the semicolon at the beginning.

// Path something from global scope.
;(function () {
  // tagsInput is kept only inside this scope.
  var tagsInput = angular.module('ngTagsInput')
  tagsInput.factory('tiTranscludeAppendDirective', function() {
      return function() {}
  })
})()

1.6.3. Defining classes

In JS there is no strict way of defining a class and instances are created using a function and new operator.

When defining a class we use an anonymous function to allow class private instances and create a new class scope.

var BaseAccount = (function() {

    var class_private_member = 2

    /*
    Constructor is here.
    */
    var cls = function(name, age) {
        this.name = name
        this.age = age
    }

    cls.prototype.class_member = 3

    /*
    Base method.
    */
    cls.prototype.base_method = function() {
        return this.name + '-' + this.age
    }

    /*
    Some method.
    */
    cls.prototype.some_method = function(prefix) {
        return prefix + this.base_method()
    }

    /*
    Another method.
    */
    cls.prototype.tuned = function() {
        return false
    }

    return cls
}())


var SpecialAccount = (function() {

    var cls = function(name, age) {
        this.variant = 'light'
        /* Something similar to super()*/
        BaseAccount.call(this, name, age)
    }

    /* Something similar to inheritance. */
    cls.prototype = Object.create(BaseAccount.prototype)
    cls.prototype.constructor = cls

    /*
    Method extending parent.
    */
    cls.prototype.some_method = function(prefix) {
        var parent = BaseAccount.prototype.some_method.call(this, prefix)
        return prefix + '-child-' + parent
    }

    /*
    Method overwriting parent.
    */
    cls.prototype.tuned = function() {
        return true
    }

    return cls
}())

1.6.4. CSS interaction

1.6.4.2. Changing CSS/HTML from JS

Don’t modify the associated CSS properties, but rather modify the CSS class:

GOOD:

$('#element_id').addClass('highlight');

BAD:

$('#element_id').css('font-weight': 'bold');

Same story as with CSS, don’t modify HTML tag attributes, but rather try to change the CSS class:

GOOD:

$('#element_id').addClass('sprite red_dot');

BAD:

$('#element_id').attr('src': 'some/red_dot.png');

1.6.5. Test styleguide

  • We use expect style testing.
  • Leave 2 emtpy lines before each suite and one empty line before each test
/*
Tests for login controller.
*/

suite('LoginCtrl', function() {

    // Shared variables.
    var scope
    var ctrl

    setup(function() {
        // Initialize first.
    })

    teardown(function() {
        // Clean second.
    })

    test(
    'Initializes with no errors and blank values' +
    'long line are wrapped',
    function() {
        var something = Something()

        something.doSomething()

        assert.equal('', something.username)
    })


    suite('critical_error attribute', function(){

        test(
        'When set, hides the form and sets the error message.',
        function(){
            var message = manu.makeUniqueString()

            scope.critical_error = message
            scope.$digest()

            assert.isFalse(scope.show_form)
            assert.equal(message, scope.alert.error)
        })
    })
})