Convert string to json javascript

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:

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

Make sure the text is 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;
</script>

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Array as JSON

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

Example

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

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Exceptions

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.name + ", " + obj.birth;

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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:

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.name + ", " + obj.birth;

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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:

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.name + ", " + obj.age();

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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.

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);

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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);

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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;

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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);

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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);

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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);

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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.

Can we convert string to JSON in JavaScript?

Can I JSON Stringify a string?

How should you convert this string into a JavaScript object?

Which method converts a JSON string to a JavaScript object?