JavaScript Object and JSON

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JavaScript Object

A JavaScript is wrapped by {} or created by new. Components inside are like key:value pairs.

i.e. JavaScript objects are containers for named values.

An example of JavaScript Object:

var car = {
            type: "Fiat",
            model: 500,
            color: "silver",
            buycar: function(money){
                return money * 115%;

Each JavaScript has properties and methods.


In the example above, type, model and color are properties. You can access properties by using object_name.property_name to get value of certain property.

car.type //'Fiat'

A JavaScript object has two build-in properties: length and prototype


You can create methods in a JavaScript object. In code above, butcar is a method. A method can be defined by a function.

A method may or may not have parameters A method may or may not have return values

car.buycar(100) //115

A JavaScript object has a list of build-in method. You can view them here.


  1. To change JSON to JavaScript object, you can use JSON.parse(json_object) or jQuery method: $.parseJSON(json_object)

  2. String, Number and Boolean should not be declared as objects, which means code like var x = new String() is not recommended.


JSON means JavaScript Object Notation. It has following rules:

  • Data is in name/value pairs

  • Data is separated by commas ,

  • Curly braces {} hold objects

  • Square brackets [] hold arrays

To operate JSON, you can change a JSON to a JavaScript object, then use properties and methods of that JavaScript object.

Example of JSON:

var text =  '{ "employees" : [' +
            '{ "firstName":"John" , "lastName":"Doe" },' +
            '{ "firstName":"Anna" , "lastName":"Smith" },' +
            '{ "firstName":"Peter" , "lastName":"Jones" } ]}';
* 1. This JSON has a large JavaScript object, which has a property: 'employees'
* 2. The value of the 'employees' property is an JavaScript objects array.
* 3. The array has four JavaScript objects, each object has two properties: 'firstName' and 'lastName', with property values.


  1. To change a JavaScript objec to JSON, using JSON.stringify(js_object)
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