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JSON.parse()

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.

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:

<p id="demo"></p>

<script>

document.getElementById("demo").innerHTML = obj.name;

</script>

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

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

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:

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;

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.

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;

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:

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();

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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