CODEWITHSUNDEEP
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cybertextron
cybertextron

Reputation: 10971

Why does JavaScript have different declarations for the same behavior?

Why should I declare

var foo = {}

instead of 

var foo = new Object();

in JavaScript if they are similar? Does the same applies to

foo[0].bar = new Function(){ "return hello"};

as in in

foo[0].bar = function(){return "hello"};

? Is it an efficiency matter? Does it make difference?

Upvotes: 2

Views: 89

Answers (5)

The Alpha
The Alpha

Reputation: 146201

Actually 

var foo = {}

and

var foo = new Object();

does the same thing (both expressions create an empty Object) but it's better to use shorter version (object literal), it takes less space time to write and another thing that using object literal you can create and assign values/properties to an Object as follows

person = {
    property1 : "Hello"
};

but using new Object() you need to create it first and then assign values/properties as follows

person = new Object();
person.property1 = "Hello";

In your second example (function vs new function) there is a difference because new Function is slower and you can take a look at this test here.

Upvotes: 2

LetterEh
LetterEh

Reputation: 26696

The new Function() constructor doesn't really work that way.

It's called like:

var myFunc = new Function("param1", "param2", "message", "/*function-body-as-a-string*/ console.log(message); return param1 + \"=\" + param2;");

ie: really dumb, error-prone, stupid-slow (uses eval) and a security-hole. Don't use it.

Upvotes: 0

Uncle Iroh
Uncle Iroh

Reputation: 6055

I remember reading the following from w3fools.com:

personObj=new Object();

This is a bad and unnecessary use of the new keyword. They should be using and advocating the object literal syntax ({}) for creating new objects.

It doesn't say why, only that we should.

Upvotes: 2

whiskeyfur
whiskeyfur

Reputation: 746

The only times it might matter is if your writing a program that generates such javascript dynamically ... or your writing for a certain teacher in college who seems to have a certain standard that doesn't quite make sense at times.

Upvotes: 0

dano
dano

Reputation: 1043

No there isn't any efficiency increase or decrease, its just shorthand like using ? : for if/else..

I always use shorthand {} but if you are going to have a beginner reading your code you may want to use new Object().

Upvotes: 0

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