Question

Could you guys please explain the difference between the two following variables?

var test = {};
var test2 = [];

Are they not both declaring an array variable? If not, when to use which?

Answer 1

The first creates an object (empty object with no properties at all).

The second creates an empty array.

Let’s take an example of manipulating an object:

var test = { firstName: 'Foo', lastName: 'Bar' };
alert(test.firstName);

you could also dynamically extend an existing empty object and add properties to it:

var test = {  };
test.firstName = 'Foo'; // or an equivalent: test['firstName'] = 'Foo';
alert(test.firstName);

and an array:

var test2 = [ { firstName: 'Foo', lastName: 'Bar' }, 
              { firstName: 'Foo 2', lastName: 'Bar 2' } ];
for (var i = 0; i < test2.length; i++) {
    alert(test2[i].firstName);
}

or to add elements to an array:

var test = { firstName: 'Foo', lastName: 'Bar' };
var test2 = [ ];
test2.push(test); // the array contains 1 element now
alert(test2[0].firstName);