freeCodeCamp/guide/english/javascript/standard-objects/json/json-parse/index.md

title
JSON Parse

JSON Parse

The JSON.parse() method parses a string and construct a new object described by a string.

Syntax:

    JSON.parse(text [, reviver])

Parameters:

text The string to parse as JSON

reviver(Optional) The function will receive key and value as arguments. This function can be used to tranform the result value.

Here is an example on how to use JSON.parse():

var data = '{"foo": "bar"}';

console.log(data.foo); // This will print `undefined` since `data` is of type string and has no property named as `foo`

// You can use JSON.parse to create a new JSON object from the given string
var convertedData = JSON.parse(data);

console.log(convertedData.foo); // This will print `bar

Repl.it Demo

Here is an example with reviver:

var data = '{"value": 5}';

var result = JSON.parse(data, function(key, value) {
    if (typeof value === 'number') {
        return value * 10;
    }
    return value;
});

// Original Data
console.log("Original Data:", data); // This will print Original Data: {"value": 5}
// Result after parsing
console.log("Parsed Result: ", result); // This will print Parsed Result:  { value: 50 }

In the above example, all numberic values are being multipled by 10 - Repl.it Demo

More Information:

JSON.parse - MDN