JavaScript - run a function once DOM has loaded, or straightaway if already loaded

gistfile1.js

document.addEventListener("DOMContentLoaded", DomIsLoaded, false);
//readystate :: loading --> interactive (document.DOMContentLoaded) --> complete (window.load) 
if (document.readyState === "complete" || document.readyState === "interactive") {
    document.removeEventListener("DOMContentLoaded", DomIsLoaded);
    DomIsLoaded();
}

// usage----------------->
function DomIsLoaded() {
    // do stuff once DOM has loaded
}

Sometimes it is useful to run a JavaScript function as soon as possible, but not before the DOM has loaded.
This script creates an event listener, but if DOM is already loaded, it will delete the event handler and execute the handler straight away.