Question

I have this code

window.onload = function() {            
    function foo() {
        alert("test");
    }
    setInterval("foo()",500)
}

Which returns undefined…When i use it outside the window.onload it works. Can anyone explain me why?

Answer 1

Using a string command in setInterval() will try to look for the function in the global (window) scope, but since the function is defined in a local scope, it won’t be found. You should pass the function itself to setInterval() instead.

window.onload = function() {            
    function foo() {
        alert("test");
    }
    setInterval(foo, 500);
}