Callback function in javascript

Question

What is the problem with this code

var a=function()
{
   setInterval(function(){document.write("a");},1000);
}

function b(callback)
{
    callback();
    alert(2);
}

b(a); // alert 2

It should not not show me the alert because the call not over yet?

Answer 1

You could add the callback into your setInterval function so that it doesn't get executed until after the 1000 millisecond delay, e.g:

    var a=function(callback) {
        setInterval(function(){document.write("a"); callback(); },1000);
    }

    function b() {
        alert(2);
    }

a(b); // alert 2 AFTER the 1000 millisecond delay

Answer 2

The code is running as expected. SetInterval doesn't hold the execution for rest of the code it fires assigned function after specified time.

So you will get alert and then document.write.