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> 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(); 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(); 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; 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; var text = '{ "name":"John", "age":"function () {return 30;}", "city":"New York"}';
var obj = JSON.parse(text);
obj.age = eval("(" + obj.age + ")");
document.getElementById("demo").innerHTML = obj.name + ", " + obj.age();
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.
The numbers in the table below specifies the first browser version that fully supports the JSON.parse() function:
| Chrome | Internet explorer | Mozila Firefox | Safari | Opera |
|---|---|---|---|---|
| Yes | 8.0 | 3.5 | 4.0 | 10.0 |
