Question

I am using a Javascript function do_when to keep evaluating another function and perform an action once it returns true. I found the function here: javascript, wait for something to be true then run action

Here is the do_when function:

function do_when(predicate, action, timeout_step) {
    if (predicate()) {
        action();
    } else {
        setTimeout(do_when, timeout_step, predicate, action, timeout_step);
    }
}

I am using it to call a jQuery function:

do_when(function() {return tabledrawn;},
    function() {$("#mytable tbody tr td").first().click();}, 
    100);

Everything works fine in Firefox and Chrome, but IE9 (and earlier) fails. Specifically, I get an “Object Expected” error when do_when is called from the setTimeout function.

When I do a debug, the predicate and action arguments correctly show up as function objects when do_when is initially called, but when it is called again from the setTimeout function they both show up as undefined. It appears I am not supplying the arguments to setTimeout the way IE wants to see them. Is there a proper way in IE to pass a function object and its parameters as arguments?

EDIT:
Per SLaks suggestions I changed do_when to the following:

function do_when(predicate, action, timeout_step) {
    if (predicate()) {
        action();
    } else {
        setTimeout(function () {
                       do_when(predicate, action, timeout_step);
                   }, 
                   timeout_step);
    }
}

Which fixes my problem.

Answer 1

You’re passing additional arguments to setTimeout, and you’re expecting them to be passed to your function.

That’s a non-standard Mozilla-only feature.

Instead, you need to pass an anonymous function to setTimeout, and call your function with whatever arguments you want inside of it.