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6.9 Serializing Objects

6.9 Serializing Objects

Object serialization is the process of converting an object’s state to a string from which it can later be restored. ECMAScript 5 provides native functions JSON.stringify() and JSON.parse() to serialize and restore JavaScript objects. These functions use the JSON data interchange format. JSON stands for “JavaScript Object Notation,” and its syntax is very similar to that of JavaScript object and array literals:

o = {x:1, y:{z:[false,null,""]}}; // Define a test object s = JSON.stringify(o); // s is '{"x":1,"y":{"z":[false,null,""]}}' p = JSON.parse(s); // p is a deep copy of o

The native implementation of these functions in ECMAScript 5 was modeled very closely after the public-domain ECMAScript 3 implementation available at http://json .org/json2.js . For practical purposes, the implementations are the same, and you can use these ECMAScript 5 functions in ECMAScript 3 with this json2.js module.

JSON syntax is a subset of JavaScript syntax, and it cannot represent all JavaScript values. Objects, arrays, strings, finite numbers, true, false, and nullare supported and can be serialized and restored. NaN, Infinity, and -Infinity are serialized to null. Date objects are serialized to ISO-formatted date strings (see the Date.toJSON() function), but JSON.parse() leaves these in string form and does not restore the original Date object. Function, RegExp, and Error objects and the undefined value cannot be serialized or restored. JSON.stringify() serializes only the enumerable own properties of an object. If a property value cannot be serialized, that property is simply omitted from the stringified output. Both JSON.stringify()and JSON.parse()accept optional second arguments that can be used to customize the serialization and/or restoration process by specifying a list of properties to be serialized, for example, or by converting certain values during the serialization or stringification process. Complete documentation for these functions is in the reference section.

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