Why would you invoke new Date without parentheses? [duplicate]

Question

I have just seen this snippet while accidentally opening dev tools in Gmail:

var GM_TIMING_END_CHUNK1=(new Date).getTime(); 

I would usually expect something like this, as it's rather uncommon to invoke a constructor without parentheses (at least I have never seen it until now):

var GM_TIMING_END_CHUNK1=new Date().getTime(); 

or

var GM_TIMING_END_CHUNK1=Date.now(); //newer browsers 

Is there any advantage in doing so, any difference in behavior? It's the exact same amount of characters needed, so brevity won't be a reason.

Answer 1

You can invoke constructors in JS w/o the parenthesis if no parameters are to be passed, the effect is the same.

new Date() vs new Date the same.

However, it makes a difference when you want to call a method on the resulting object:

new Date().getTime() works but new Date.getTime() would not because in the latter case the interpreter assumes getTime is a method of the Date type but that's not true, getTime is an instance method - only exists in constructed objects. To overcome this you can wrap parenthesis around the constructor call to tell the interpreter that it is an expression:

(new Date).getTime()

This way first the expression is evaluated and getTime is called on the result which is an instance of Date.