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6.1.1 Object Literals

6.1.1 Object Literals


The easiest way to create an object is to include an object literal in your JavaScript code. An object literal is a comma-separated list of colon-separated name:value pairs, enclosed within curly braces. A property name is a JavaScript identifier or a string literal (the empty string is allowed). A property value is any JavaScript expression; the value of the expression (it may be a primitive value or an object value) becomes the value of the property. Here are some examples:

var empty = {}; // An object with no properties var point = { x:0, y:0 }; // Two properties var point2 = { x:point.x, y:point.y+1 }; // More complex values var book = {

"main title": "JavaScript", // Property names include spaces, 'sub-title': "The Definitive Guide", // and hyphens, so use string literals "for": "all audiences", // for is a reserved word, so quote author: { // The value of this property is

firstname: "David", // itself an object. Note that surname: "Flanagan" // these property names are unquoted. } };

In ECMAScript 5 (and some ECMAScript 3 implementations), reserved words may be used as property names without quoting. In general, however, property names that are reserved words must be quoted in ECMAScript 3. In ECMAScript 5, a trailing comma following the last property in an object literal is ignored. Trailing commas are ignored in most ECMAScript 3 implementations, but IE considers them an error.

An object literal is an expression that creates and initializes a new and distinct object each time it is evaluated. The value of each property is evaluated each time the literal is evaluated. This means that a single object literal can create many new objects if it appears within the body of a loop in a function that is called repeatedly, and that the property values of these objects may differ from each other.

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