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JSON Parse

JSON is commonly used 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 is a JavaScript object.

Example – Parsing JSON

Imagine that we have 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 on your page:

Example

<!DOCTYPE html>

<html>

<body>

<h2>Creating an Object from a JSON String</h2>

<p id=”demo”></p>

<script>

const txt = ‘{“name”:”John”, “age”:30, “city”:”New York”}’

const obj = JSON.parse(txt);

document.getElementById(“demo”).innerHTML = obj.name + “, ” + obj.age;

</script>

</body>

</html>

Output

Creating an Object from a JSON String

Array as JSON

Using the JSON.parse() on a JSON derived from an array, the method is used to return a JavaScript array, instead of a JavaScript object.

Example

<!DOCTYPE html>

<html>

<body>

<h2>Parsing a JSON Array.</h2>

<p>Data written as a JSON array will be parsed into a JavaScript array.</p>

<p id=”demo”></p>

<script>

const text = ‘[ “Ford”, “BMW”, “Audi”, “Fiat” ]’;

const myArr = JSON.parse(text);

document.getElementById(“demo”).innerHTML = myArr[0];

</script>

</body>

</html>

Output

Parsing a JSON Array.

Data written as a JSON array will be parsed into a JavaScript array.

Ford

Exceptions

Parsing Dates

Date objects are not permitted in JSON.

To include a date, write it as a string.

You can convert it back into a date object later:

Example

<!DOCTYPE html>

<html>

<body>

<h2>Convert a string into a date object.</h2>

<p id=”demo”></p>

<script>

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;

</script>

</body>

</html>

Output

Convert a string into a date object.

John, Sun Dec 14 1986 05:30:00 GMT+0530 (India Standard Time)

you can use the second parameter, of the JSON.parse() function, called reviver.

The reviver parameter is a function that goes through each property, before returning the value.

Example

<!DOCTYPE html>

<html>

<body>

<h2>Convert a string into a date object.</h2>

<p id=”demo”></p>

<script>

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;

</script>

</body>

</html>

Output

Convert a string into a date object.

John, Sun Dec 14 1986 05:30:00 GMT+0530 (India Standard Time)


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