Dean Dean - 3 months ago 9x
Javascript Question

In JavaScript, does it make a difference if I call a function with parentheses?

I noticed a difference when calling a function with empty parentheses, or without any parentheses at all. However, I am not passing any arguments to the function so I wondered, what would be the difference between:

window.onload = initAll();


window.onload = initAll;

Please explain the principle behind it.

Thanx in advance.


window.onload = initAll();

This executes initAll() straight away and assigns the function's return value to window.onload. This is usually not what you want. initAll() would have to return a function for this to make sense.

window.onload = initAll;

this assigns the actual function to window.onload - this is possible because in JavaScript, as @Felix says, functions are first class objects - without executing it. initAll will be executed by the load event.