函数没有正确计算元素的数量

Question

我使用Brock Adams 的waitForKeyElements 函数在https://www.google.com/ 上的链接之后创建复选框。

由于某种原因，该功能无法正常工作。它不是在每个链接之后放置单个复选框，而是计算所有链接，然后在每个链接之后添加相应数量的复选框。

可能是什么错误？

// ==UserScript==
// @grant   none
// @match   https://*.google.*/
// @name    Google.com
// @require https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js
// @require https://gist.githubusercontent.com/BrockA/2625891/raw/9c97aa67ff9c5d56be34a55ad6c18a314e5eb548/waitForKeyElements.js
// ==/UserScript==

(function() {
    'use strict';

    function test() {
        var links = document.querySelectorAll('a');
        var i;
        for (i = 0; i < links.length; i++) {
            var input = document.createElement('input');
            input.type = 'checkbox';
            links[i].parentElement.appendChild(input);
        }
    }

    //waitForKeyElements('a', test); // works incorrectly. The third parameter
        // doesn't help.
    //setTimeout(test(), 3000); // works OK
})();

函数本身：

/*--- waitForKeyElements():  A utility function, for Greasemonkey scripts,
    that detects and handles AJAXed content.

    Usage example:

        waitForKeyElements (
            "div.comments"
            , commentCallbackFunction
        );

        //--- Page-specific function to do what we want when the node is found.
        function commentCallbackFunction (jNode) {
            jNode.text ("This comment changed by waitForKeyElements().");
        }

    IMPORTANT: This function requires your script to have loaded jQuery.
*/
function waitForKeyElements (
    selectorTxt,    /* Required: The jQuery selector string that
                        specifies the desired element(s).
                    */
    actionFunction, /* Required: The code to run when elements are
                        found. It is passed a jNode to the matched
                        element.
                    */
    bWaitOnce,      /* Optional: If false, will continue to scan for
                        new elements even after the first match is
                        found.
                    */
    iframeSelector  /* Optional: If set, identifies the iframe to
                        search.
                    */
) {
    var targetNodes, btargetsFound;

    if (typeof iframeSelector == "undefined")
        targetNodes     = $(selectorTxt);
    else
        targetNodes     = $(iframeSelector).contents ()
                                           .find (selectorTxt);

    if (targetNodes  &&  targetNodes.length > 0) {
        btargetsFound   = true;
        /*--- Found target node(s).  Go through each and act if they
            are new.
        */
        targetNodes.each ( function () {
            var jThis        = $(this);
            var alreadyFound = jThis.data ('alreadyFound')  ||  false;

            if (!alreadyFound) {
                //--- Call the payload function.
                var cancelFound     = actionFunction (jThis);
                if (cancelFound)
                    btargetsFound   = false;
                else
                    jThis.data ('alreadyFound', true);
            }
        } );
    }
    else {
        btargetsFound   = false;
    }

    //--- Get the timer-control variable for this selector.
    var controlObj      = waitForKeyElements.controlObj  ||  {};
    var controlKey      = selectorTxt.replace (/[^\w]/g, "_");
    var timeControl     = controlObj [controlKey];

    //--- Now set or clear the timer as appropriate.
    if (btargetsFound  &&  bWaitOnce  &&  timeControl) {
        //--- The only condition where we need to clear the timer.
        clearInterval (timeControl);
        delete controlObj [controlKey]
    }
    else {
        //--- Set a timer, if needed.
        if ( ! timeControl) {
            timeControl = setInterval ( function () {
                    waitForKeyElements (    selectorTxt,
                                            actionFunction,
                                            bWaitOnce,
                                            iframeSelector
                                        );
                },
                300
            );
            controlObj [controlKey] = timeControl;
        }
    }
    waitForKeyElements.controlObj   = controlObj;
}

Answer 1

您没有提供waitForKeyElements 的用例，但如果我理解正确，您将test 函数传递给它。如果是这种情况 - 难怪它会在页面上的每个链接上附加 X 复选框。仔细看：
- 您的函数在被调用时会搜索页面中的所有链接并在其旁边添加一个复选框
- waitForKeyElements 根据提供的选择器为它找到的每个元素调用该函数。 所以，基本上，如果页面有 50 个链接，if 将在每个链接后附加一个复选框 50 次。

解决方案是不要在你的函数中循环，而是只在提供的参数中添加一个复选框：

(function() {
    'use strict';

    function test(element) {
        var input = document.createElement('input');
        input.type = 'checkbox';
        element.parent().append(input);
    }
})();