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JSON.stringify()

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

When sending data to a web server, the data has to be a string.

Convert a JavaScript object into a string with JSON.stringify().

Stringify a JavaScript Object

Imagine we have this object in JavaScript:

const obj = {name: "John", age: 30, city: "New York"};

Use the JavaScript function JSON.stringify() to convert it into a string.

const myJSON = JSON.stringify(obj);

The result will be a string following the JSON notation.

myJSON is now a string, and ready to be sent to a server:

Example

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

You will learn how to send JSON to a server in the next chapters.

Stringify a JavaScript Array

It is also possible to stringify JavaScript arrays:

Imagine we have this array in JavaScript:

const arr = ["John", "Peter", "Sally", "Jane"];

Use the JavaScript function JSON.stringify() to convert it into a string.

const myJSON = JSON.stringify(arr);

The result will be a string following the JSON notation.

myJSON is now a string, and ready to be sent to a server:

Example

const arr = ["John", "Peter", "Sally", "Jane"];
const myJSON = JSON.stringify(arr);

You will learn how to send a JSON string to a server in the next chapters.

Storing Data

When storing data, the data has to be a certain format, and regardless of where you choose to store it, text is always one of the legal formats.

JSON makes it possible to store JavaScript objects as text.

Example

Storing data in local storage

// Storing data:
const myObj = {name: "John", age: 31, city: "New York"};
const myJSON = JSON.stringify(myObj);
localStorage.setItem("testJSON", myJSON);

// Retrieving data:
let text = localStorage.getItem("testJSON");
let obj = JSON.parse(text);
document.getElementById("demo").innerHTML = obj.name;

Exceptions

Stringify Dates

In JSON, date objects are not allowed. The JSON.stringify() function will convert any dates into strings.

Example

const obj = {name: "John", today: new Date(), city : "New York"};
const myJSON = JSON.stringify(obj);

You can convert the string back into a date object at the receiver.

Stringify Functions

In JSON, functions are not allowed as object values.

The JSON.stringify() function will remove any functions from a JavaScript object, both the key and the value:

Example

const obj = {name: "John", age: function () {return 30;}, city: "New York"};
const myJSON = JSON.stringify(obj);

This can be omitted if you convert your functions into strings before running the JSON.stringify() function.

Example

const obj = {name: "John", age: function () {return 30;}, city: "New York"};
obj.age = obj.age.toString();
const myJSON = JSON.stringify(obj);

If you send functions using JSON, the functions will lose their scope, and the receiver would have to use eval() to convert them back into functions.


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