JavaScript JSON Object

JSON Object Literals

This is a JSON string:

'{"name":"John", "age":30, "car":null}'

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Inside the JSON string is a JSON object literal:

{"name":"John", "age":30, "car":null}

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JSON Object Literals

• Surrounded by curly braces {}.
• Contain key/value pairs.
• Keys and values are separated by a colon.
• Keys must be strings, and values must be a valid JSON data type: string, number, object, array, boolean, null.
• Each key/value pair is separated by a comma.

It is a common mistake to call a JSON object literal "a JSON object." JSON is a string format. When converted to a JavaScript variable, it becomes a JavaScript object.

JavaScript Objects

You can create a JavaScript object from a JSON object literal:

const myObj = {"name": "John", "age": 30, "car": null};

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Normally, you create a JavaScript object by parsing a JSON string:

const myJSON = '{"name":"John", "age":30, "car":null}';
const myObj = JSON.parse(myJSON);

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Accessing Object Values

Using dot notation:

const x = myObj.name;

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Using bracket notation:

const x = myObj["name"];

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Looping Through an Object

You can loop through object properties with a for-in loop:

let text = "";
for (const key in myObj) {
  text += key + ", ";
}

In a for-in loop, use bracket notation to access property values:

let text = "";
for (const key in myObj) {
  text += myObj[key] + ", ";
}