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I've never understood the application of return true and return false after function calls in JavaScript. Could somebody please explain their meaning. This is a very simple script which will create a popup window for each links in an html document. function createPopup(e) { 'use strict'; // Get the event object: if (typeof e == 'undefined') var e = window.event; // Get the event target: var target = e.target || e.srcElement; // Create the window: var popup = window.open(target.href, 'PopUp', 'height=100,width=100,top=100,left=100,location=no,resizable=yes,scrollbars=yes'); // Give the window focus if it's open: if ( (popup !== null) && !popup.closed) { popup.focus(); return false; // Prevent the default behavior. } else { // Allow the default behavior. return true; } } // End of createPopup() function. // Establish functionality on window load: window.onload = function() { 'use strict'; // Add the click handler to each link: for (var i = 0, count = document.links.length; i < count; i++) { document.links[i].onclick = createPopup; } // End of for loop. }; // End of onload function. The only part of the script that doesn't make sense here is the return true/false. Why do we use return true or return false after calling a JavaScript function?