In JavaScript, does it make a difference if I call a function with parentheses?
javascript
Solution
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.
You may also see something like this:
window.onload = () => initAll();
This will create a new function that, when called, will call `initAll` immediately. Parentheses are necessary here for that "call `initAll` immediately" part to work. But, because it's wrapped in a function, nothing will execute until that outer function itself is called, and you assign the reference of that outer function to `window.onload`, so `initAll` will also be executed on the load event.
Problem
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(); ``` and ``` window.onload = initAll; ``` Please explain the principle behind it.