JSON.parse() Parsing

JSON is used for data exchange with web servers. When data is received from a web server, it is always a string.

The JSON.parse() method parses a JSON string to construct JavaScript values or the object described by the string.

Syntax:

JSON.parse(text, reviver)

The first parameter specifies the string to be parsed as JSON.

The optional second parameter specifies a function to check each property before the return value.

Parse JSON

Suppose we receive the following text from the web server:

　22, "city":"New Delhi"

Using the JSON.parse() method, we can convert JSON text to a JavaScript object:

22, "city":"New Delhi"

JSON from the server

You can use AJAX requests to request JSON from the server.

If the response from the server is written in JSON format, the string can be parsed into a JavaScript object.

The following example requests the filedemo.jsonand parse the response:

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

Array as JSON

JSON.parse() is used on JSON derived from arrays, which will return a JavaScript array instead of a JavaScript object.

The following example requests the filejson_array.txtand parse the response:

var httpRequest = new XMLHttpRequest();
httpRequest.onreadystatechange = function() {
　　　if (this.readyState ===　4　&& this.status ===　200) {
　　　　　　var myArr = JSON.parse(this.responseText);
　　　　　　document.getElementById("output").innerHTML = myArr[0];
　　　}
};
httpRequest.open("GET", "json_array.txt", true);
httpRequest.send();

Parsing Dates

Date objects are not allowed in JSON.

If you need to include dates, write them as strings and then convert them back to date objects later.

var myJSON = '{"name":"Seagull", "birth":"1997-11-10", "city":"New Delhi"}';
var myObj = JSON.parse(myJSON);
myObj.birth = new Date(myObj.birth);
document.getElementById("output").innerHTML = myObj.name　+　"　DOB　is　"　+　myObj.birth;

Note: Converting a string into a local object is calledParsing, and converts a local object into a format that can be transmitted over the network.Stringis calledStringification.