Why I can't directly set console.log() as callback function

Question

Why this code doesn\'t work

function callback(num, func) {
    for(var i = 0; i < num; i++) {
        func();
    }
}

callback(4, console.log(\"Hello         


        

Answer 1

Because functions are first-class citiziens in Javascript (meaning functions can be stored in variables). passing a function as an argument will return a reference to the function definition rather than the function call you're trying to invoke. It does however evaluate your console.log beforehand and passes it on as a variable and since your log's function call doesn't return anything it passes undefined to your callback function.

function test( logFunction ){
    logFunction( 'test' )
}

test( alert )

Is an example of this behaviour. It's also the reason closures like the one demonstrated by Remy J work.

function callback(num, func) {
    for(var i = 0; i < num; i++) {
        func( "Hello" );
    }
}

callback(4, alert);

This would work.