conversant/ad-libs.js

'use strict';

// Take care when listening for 'interactive' since things can be wonky in IE unless checking 'complete' only
// https://connect.microsoft.com/IE/feedback/details/792880/document-readystate-interactive-firing-too-early-misfiring-in-ie11-9-and-10

var domReady = function (callback, targetWindow, isInteractiveOk) {

    // Local variables, because domReady should work for more than just the parent document/window
    var hasLoaded = false,
        pollingTimeoutHandle,
        win = targetWindow || window,
        doc = win.contentDocument || win.document;

    var checkDoc = function () {
        return (doc.readyState === 'interactive' && !!isInteractiveOk) || doc.readyState === 'complete';
    };

    var pollReadiness = function (callback) {
        if (checkDoc() && !hasLoaded) { // The state of the doc is ready, but this was somehow missed by the event handlers
            hasLoaded = true;
            callback();
        } else if (!hasLoaded) { // This check will drop us out of this checking loop if we fail
            pollingTimeoutHandle = setTimeout(function () {
                pollReadiness(callback);
            }, 10);
        }
    };

    var signalReadiness = function (callback) {
        if (!hasLoaded) {
            hasLoaded = true;

            if (pollingTimeoutHandle) {
                clearTimeout(pollingTimeoutHandle);
            }
            callback();
        }
    };

    if (hasLoaded || checkDoc()) {
        signalReadiness(callback);
    } else {
        if (doc.addEventListener) {
            // IE9+, Firefox, Chrome, Safari
            doc.addEventListener('DOMContentLoaded', function() { // same as interactive readyState
                if (checkDoc()) {
                    signalReadiness(callback);
                }
            }, false);
            // IE, old Safari
            win.addEventListener('load', function() { // same as complete readyState
                signalReadiness(callback);
            }, false);
            // IE 8
        } else if (doc.attachEvent) {
            doc.attachEvent('onreadystatechange', function() { // can be any readyState
                if (checkDoc()) {
                    signalReadiness(callback);
                }
            });
            doc.attachEvent('onLoad', function() { // same as complete readyState
                signalReadiness(callback);
            });
        }

        // For scripts using the "async" attribute, they'll execute AFTER the synchronous scripts load in sequence. This
        // can cause a race condition where the DOMContentLoaded event will fire, but the script itself becomes unaware
        // it happened. Because this is problematic even in modern browsers like chrome, it's important to have a fallback
        // polling check which will cancel itself once the page finishes loading.
        pollReadiness(callback);
    }

};

/**
 * @module domReady
 * @desc Executes the provided callback when the DOM is ready. Allows code to act on the DOM before the window "load" event fires.
 * @param {Function} callback
 * @param {Window} [targetWindow] You can provide your own window reference for cases where you'd have an iframe.
 * @param {Boolean} [isInteractiveOk] Interactive mode can be checked for faster responses.
 * @example
 * ```js
 * var domReady = require('adlibs/lib/dom/domReady');
 *
 * // executes the cb on dom ready
 * domReady(cb, window);
 *
 * ```
 */
module.exports = domReady;