Learning from jQuery by Callum Macrae

Author:Callum Macrae
Language: eng
Format: epub, pdf
Tags: COMPUTERS / Programming Languages / JavaScript
ISBN: 9781449345259
Publisher: O’Reilly Media
Published: 2012-08-22T16:00:00+00:00

Literals Notation

JavaScript has literal notations available for stuff like creating new objects and arrays, which allow you to shorten your code and make it clearer. It is better to use literals than the constructor functions, such as new Object() and new Array(), and I’ll explain why using a few examples.

Object Literals

The object literal simply uses curly braces. Here are two ways of defining exactly the same object:

// Using the literal syntax var obj = {}; // Using the constructor function (antipattern) var obj = new Object();

The most obvious reason to use the literal syntax instead of the constructor function is that it is shorter to type, but there are a couple more reasons. The literal syntax never has scoping issues—if, for example, you accidentally call a variable Object, you would overwrite the object constructor, and you would not be able to create any more objects using the constructor function. This can never happen to the literal syntax. In a similar vein, the parser doesn’t have to do any scope resolution with the literal syntax. If you use the literal syntax, JavaScript knows exactly what you mean and gives you an object. If you use the constructor function, however, then JavaScript has to check the current scope, then cycle up through the parent scopes until it finds the Object constructor. The first uses fewer resources and is slightly quicker. Finally, you can declare properties using the literal notation:

// Using the literal syntax var obj = { foo: 'bar', hello: 'world' }; // Using the constructor function (antipattern) var obj = new Object(); obj.foo = 'bar'; obj.hello = 'world';

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