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JSON .parse()


A common use of JSON is to exchange data to/from a web server.

When receiving data from a web server, the data is always a string.

Parse the data with JSON.parse(), and the data becomes a JavaScript object.


Example – Parsing JSON

Imagine we received this text from a web server:

‘{ “name”:”John”, “age”:30, “city”:”New York”}’

Use the JavaScript function JSON.parse() to convert text into a JavaScript object:

var obj = JSON.parse(‘{ “name”:”John”, “age”:30, “city”:”New York”}’);

Make sure the text is written in JSON format, or else you will get a syntax error.

Use the JavaScript object in your page:

Example

<p id=”demo”></p>

<script>
document.getElementById(“demo”).innerHTML = obj.name + “, ” + obj.age;
</script>

Try it Yourself »


JSON From the Server

You can request JSON from the server by using an AJAX request

As long as the response from the server is written in JSON format, you can parse the string into a JavaScript object.

Example

Use the XMLHttpRequest to get data from the server:

var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
var myObj = JSON.parse(this.responseText);
document.getElementById(“demo”).innerHTML = myObj.name;
}
};
xmlhttp.open(“GET”, “json_demo.txt”, true);
xmlhttp.send();

Try it Yourself »Take a look at json_demo.txt



Array as JSON

When using the JSON.parse() on a JSON derived from an array, the method will return a JavaScript array, instead of a JavaScript object.

Example

The JSON returned from the server is an array:

var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
var myArr = JSON.parse(this.responseText);
document.getElementById(“demo”).innerHTML = myArr[0];
}
};
xmlhttp.open(“GET”, “json_demo_array.txt”, true);
xmlhttp.send();

Try it Yourself »Take a look at json_demo_array.txt


Exceptions

Parsing Dates

Date objects are not allowed in JSON.

If you need to include a date, write it as a string.

You can convert it back into a date object later:

Example

Convert a string into a date:

var text = ‘{ “name”:”John”, “birth”:”1986-12-14″, “city”:”New York”}’;
var obj = JSON.parse(text);
obj.birth = new Date(obj.birth);

document.getElementById(“demo”).innerHTML = obj.name + “, ” + obj.birth;

Try it Yourself »

Or, you can use the second parameter, of the JSON.parse() function, called reviver.

The reviver parameter is a function that checks each property, before returning the value.

Example

Convert a string into a date, using the reviver function:

var text = ‘{ “name”:”John”, “birth”:”1986-12-14″, “city”:”New York”}’;
var obj = JSON.parse(text, function (key, value) {
if (key == “birth”) {
return new Date(value);
} else {
return value;
}});

document.getElementById(“demo”).innerHTML = obj.name + “, ” + obj.birth;

Try it Yourself »

Parsing Functions

Functions are not allowed in JSON.

If you need to include a function, write it as a string.

You can convert it back into a function later:

Example

Convert a string into a function:

var text = ‘{ “name”:”John”, “age”:”function () “, “city”:”New York”}’;
var obj = JSON.parse(text);
obj.age = eval(“(” + obj.age + “)”);

document.getElementById(“demo”).innerHTML = obj.name + “, ” + obj.age();

Try it Yourself »

You should avoid using functions in JSON, the functions will lose their scope, and you would have to use eval() to convert them back into functions.


Browser Support

The JSON.parse() function is included in all major browsers and in the latest ECMAScript (JavaScript) standard:

Web Browsers Support
  • Firefox 3.5
  • Internet Explorer 8
  • Chrome
  • Opera 10
  • Safari 4

For older browsers, a JavaScript library is available at https://github.com/douglascrockford/JSON-js.