JavaScript JSON Parse
JavaScript Basics

JavaScript JSON Parse


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

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

To parse the data into a JavaScript object, use JSON.parse().

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 the text into a JavaScript object:

const obj = JSON.parse('{"name":"John", "age":30, "city":"New York"}');

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

Use the JavaScript object in your page:


<p id="demo"></p>‍<script>const obj = JSON.parse('{"name":"John", "age":30, "city":"New York"}');document.getElementById("demo").innerHTML =;</script>

Array as JSON

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


const text = '["Ford", "BMW", "Audi", "Fiat"]';const myArr = JSON.parse(text);


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:

const text = '{"name":"John", "birth":"1986-12-14", "city":"New York"}';const obj = JSON.parse(text);obj.birth = new Date(obj.birth);‍

document.getElementById("demo").innerHTML = + ", " + obj.birth;‍

Alternatively, 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:

const text = '{"name":"John", "birth":"1986-12-14", "city":"New York"}';const obj = JSON.parse(text, function (key, value) {  if (key == "birth") {    return new Date(value);  } else {    return value;  }});‍document.getElementById("demo").innerHTML = + ", " + obj.birth;‍
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 using eval(), though this is not recommended due to security concerns.

Example: Convert a string into a function:

const text = '{"name":"John", "age":"function ()

{return 30;}", "city":"New York"}';const obj = JSON.parse(text);obj.age = eval("(" + obj.age + ")");‍document.getElementById("demo").innerHTML = + ", " + 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.

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