waitForKeyElements.js

waitForKeyElements.js

/**
 * A utility function for userscripts that detects and handles AJAXed content.
 *
 * @example
 * waitForKeyElements("div.comments", (element) => {
 *   element.innerHTML = "This text inserted by waitForKeyElements().";
 * });
 *
 * waitForKeyElements(() => {
 *   const iframe = document.querySelector('iframe');
 *   if (iframe) {
 *     const iframeDoc = iframe.contentDocument || iframe.contentWindow.document;
 *     return iframeDoc.querySelectorAll("div.comments");
 *   }
 *   return null;
 * }, callbackFunc);
 *
 * @param {(string|function)} selectorOrFunction - The selector string or function.
 * @param {function}          callback           - The callback function; takes a single DOM element as parameter.
 *                                                 If returns true, element will be processed again on subsequent iterations.
 * @param {boolean}           [waitOnce=true]    - Whether to stop after the first elements are found.
 * @param {number}            [interval=300]     - The time (ms) to wait between iterations.
 * @param {number}            [maxIntervals=-1]  - The max number of intervals to run (negative number for unlimited).
 */
function waitForKeyElements(selectorOrFunction, callback, waitOnce, interval, maxIntervals) {
    if (typeof waitOnce === "undefined") {
        waitOnce = true;
    }
    if (typeof interval === "undefined") {
        interval = 300;
    }
    if (typeof maxIntervals === "undefined") {
        maxIntervals = -1;
    }
    var targetNodes = (typeof selectorOrFunction === "function")
            ? selectorOrFunction()
            : document.querySelectorAll(selectorOrFunction);

    var targetsFound = targetNodes && targetNodes.length > 0;
    if (targetsFound) {
        targetNodes.forEach(function(targetNode) {
            var attrAlreadyFound = "data-userscript-alreadyFound";
            var alreadyFound = targetNode.getAttribute(attrAlreadyFound) || false;
            if (!alreadyFound) {
                var cancelFound = callback(targetNode);
                if (cancelFound) {
                    targetsFound = false;
                }
                else {
                    targetNode.setAttribute(attrAlreadyFound, true);
                }
            }
        });
    }

    if (maxIntervals !== 0 && !(targetsFound && waitOnce)) {
        maxIntervals -= 1;
        setTimeout(function() {
            waitForKeyElements(selectorOrFunction, callback, waitOnce, interval, maxIntervals);
        }, interval);
    }
}