JSON.parse()

The conventional use of JSON is for data transmission with web servers.

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

Through JSON.parse() Parse the data, which will become JavaScript objects.

Example – Parsing JSON

Imagine that we receive this text from a web server:

'{ "name":"Bill Gates", "age":62, "city":"Seattle"}'

Please use the JavaScript function JSON.parse() Convert text to JavaScript object:

var obj = JSON.parse('{ "name":"Bill Gates", "age":62, "city":"Seattle"}');

Make sure this text is written in JSON format, otherwise there will be syntax errors.

Please use JavaScript objects on 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 AJAX requests.

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

Example

Please use XMLHttpRequest to get data from the server:

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

Try It Yourself

View json_demo.txt

as an array of JSON

when using JSON derived from an array JSON.parse() After that, this 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) {
        myArr =  JSON.parse(this.responseText);
        document.getElementById("demo").innerHTML  = myArr[0];
    }
};
xmlhttp.open("GET", "json_demo_array.txt", true);
xmlhttp.send();

Try It Yourself

See json_demo_array.txt

Exception

Parse date

Date objects are not allowed in JSON.

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

After that, you can convert it back to a date object:

Example

Convert a string to a date:

var text = '{ "name":"Bill Gates", "birth":"1955-10-28", "city":"Seattle"}
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 JSON.parse() The second parameter of the function, known as reviver.

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

Example

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

var text = '{ "name":"Bill Gates", "birth":"1955-10-28", "city":"Seattle"}';
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

Parse function

Functions are not allowed in JSON.

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

Later you can convert it back to a function:

Example

Convert a string to a function:

var text = '{ "name":"Bill Gates", "age":"function () {return 62;}", "city":"Seattle"}
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, as functions will lose their scope, and you will also need to use eval() Convert them back to functions.

Browser Support

All mainstream browsers and the latest ECMAScript (JavaScript) standards include JSON.parse() Function:

The numbers in the following table specify full support JSON.parse() The first browser version of the function:

Yes 8.0 3.5 4.0 10.0

For older browsers, the following addresses contain JavaScript libraries that are available:

https://github.com/douglascrockford/JSON-js