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>
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);
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;
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;
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();
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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