Question

what difference does it make:

function a(){
//...
}

setInterval(a, 1000);

vs

setInterval(function(){
a();
}, 1000);

Except of the obvious that I can pass parameter in the second case.

It should not necessarily be setInterval. Any function that can accept function handler.

Answer 1

Passing an anonymous function also allows you to call someObject.a() and preserve this.

If you write setTimeout(someObject.a, 300), the a() method will be called in the context of the global object, so that its this would be window. If it expects this to be someObject, it will break.

If you write setTimeout(function() { someObject.a(); }, 300), a() will be called in the correct context.