Примитивные

String

var str = 'Hello world'; 
/* use single quotes in JS */

Nubmer

var num = 1;
var num = 1.23;

Boolean

var a = true;
var a = false;

Undefined

var a = undefined; /* never do like this */
var a; /* Here a = undefined */

Null

var a = null;

Объектные

Объекты

var obj = {
    name: 'MyFirstObject',
    sayHello: function (){
        console.log('Hi, I have created an object');
    }
}
/* Get property */
obj.name /* MyFirstObject */
obj.sayHello /* function (){console.log('Hello');} */
obj.sayHello() /* Hello */
obj.age /* undefined */

/* Add property */
obj.age = 18; 
obj.age /* 18 */

Массивы

var arr = [1, 'string', true, [1,2,3], { name: 'object'}] 

arr[2] /* true */
arr.length /* 5 */