JS

JSON in Javascript

1.Create JSON

You can create it like this: 

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var foo = {
    "name" : "Ruan",
    "age"  : 25,
    "bar"  : {
        "name" : "Qiu",
        "age"  : 24
    }
}

or like this: 

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var foo = {},
    bar = {};
foo.name = "Ruan";
foo.age = 25;

bar.name = "Qiu";
bar.age = 24;

foo.bar = bar;

2.Access value in a JSON object

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console.log(foo.name); //output: Ruan
console.log(foo.bar.name); //output: Qiu

or 

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console.log(foo["name"]);
console.log(foo["bar"]["name"]);

3.Get values by loop

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for(var key in foo) {
    console.log(foo[key]);
}

Someone may say that it is exactly javascript object, so what is the difference between json and javascript object?

JSON is:

  1. It is language agnostic data-interchange format.
  2. The syntax of JSON was inspired by the JavaScript Object Literal notation, but there are differences between them.

ref:http://stackoverflow.com/questions/3975859/what-are-the-differences-between-json-and-javascript-object

For example, in JSON all keys must be quoted, while in object literals this is not necessary:

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// JSON:
{ "foo": "bar" }

// Object literal:
var o = { foo: "bar" };

Javascript object can be convered to JSON format by JSON.stringify(obj) which keys/properties names will be quoted automatically. However, it is mandatory(good behavior) to use double quotes when define a JSON object.

4.Use native JSON

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//Convert a JavaScript object into a JSON string
var jsonString = JSON.stringify(foo);
//output: {"name":"Ruan","age":25,"bar":{"name":"Qiu","age":24}}

//Convert a JSON string into a JavaScript object
var jsonObj = JSON.parse(jsonstring);
//result: a javascript object
  • NOTE: in JavaScript 1.8.5
  • Starting in JavaScript 1.8.5 (Firefox 4), JSON.parse() does not allow trailing commas
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// both will throw a SyntaxError as of JavaScript 1.8.5
var jsObject = JSON.parse("[1, 2, 3, 4, ]");
var jsObject = JSON.parse("{ \"foo\" : 1, }");