Are these way to define function in javascript equal?

I was 开发者_开发知识库wondering if the following way of writing function in javascript are equal.

To me it seems they produce the same result, but in what they can be different?

First way:

(function(){
    alert('ciao')
})();

Second way:

new function bar(){alert('ciao')}; 

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The second one returns a new instance of the function, as if it was a constructor.

So, these are equivelent:

Traditional method:

function bar() {
    this.x = 5;
};
var x = new bar();

Lazy one-liner.

var x = new function bar() { this.x = 5; };

The only difference is that you cannot reuse bar later.

If you don't believe me, try console.log(x.y); on both examples.

Your first example is an anonymous function which is not instantiated, it is just called.

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The first one executes the function and returns the result of it. The second one executes the function and returns an object.

EDIT: example: