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);
Try it Yourself »
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);
Try it Yourself »
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;
Try it Yourself »
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);
Try it Yourself »
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);
Try it Yourself »
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);
Try it Yourself »
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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Becoming certified by W3Schools is great proof to show to employers and makes your resume stand out among other candidates.
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