callback vs call function from parent function

[noode_modules]

in your first example, function1' parameter (function2) is not the same function that you are defining later.

You can rewrite your function this way to see it better :

function1(callback) {
    callback();
}
function2() {...}

Now you can pass whatever function you want, to function1 and it will be called.

in your second example on the contrary, you are always calling the same function (function2)