4

我正在使用我无法控制的 HTML 页面。<script>它在内联标记中定义了一个 Javascript 函数并在以下位置调用它<body onload="...">：

<html>
...
<body onload="init()">
<script type="text/javascript" language="javascript">
    function init() {
        ...
    }
</script>
...

如何在调用该函数之前更改它？我尝试使用 Greasemonkey 修改脚本或在其后插入另一个脚本以覆盖该函数，但它似乎没有任何效果。

4

2 回答 2

10

Greasemonkey现在通常可以通过利用事件beforescriptexecute和@run-at document-start. 请注意，似乎只有 Firefox 支持该事件，因此这不适用于 Chrome。有关更繁琐的方法，请参见此处和此处。

init()要在调用之前更改该函数，请利用checkForBadJavascripts()下面定义的函数。

你可以这样称呼它：

//--- New "init" function to replace the bad one.
function init () {
    //... Do what you want here...
}

checkForBadJavascripts ( [
    [false, /function\s+init(/, function () {addJS_Node (init);} ]
] );

wherefunction\s+init(必须是<script>您所定位的标签所独有的。（请注意，这addJS_Node()也在下面定义。）

例如，在 jsBin 访问此页面。您将看到 3 行文本，其中两行由 JS 添加。

现在，安装以下脚本并重新访问该页面。您会看到 GM 脚本删除了一个坏<script>标签，并用我们的“好”JS 替换了另一个标签。

// ==UserScript==
// @name        _Replace evil Javascript
// @include     http://output.jsbin.com/tezoni*
// @run-at      document-start
// @grant       none
// ==/UserScript==

/****** New "init" function that we will use
    instead of the old, bad "init" function.
*/
function init () {
    var newParagraph            = document.createElement ('p');
    newParagraph.textContent    = "I was added by the new, good init() function!";
    document.body.appendChild (newParagraph);
}

/*--- Check for bad scripts to intercept and specify any actions to take.
*/
checkForBadJavascripts ( [
    [false, /old, evil init()/, function () {addJS_Node (init);} ],
    [true,  /evilExternalJS/i,  null ]
] );

function checkForBadJavascripts (controlArray) {
    /*--- Note that this is a self-initializing function.  The controlArray
        parameter is only active for the FIRST call.  After that, it is an
        event listener.

        The control array row is  defines like so:
        [bSearchSrcAttr, identifyingRegex, callbackFunction]
        Where:
            bSearchSrcAttr      True to search the SRC attribute of a script tag
                                false to search the TEXT content of a script tag.
            identifyingRegex    A valid regular expression that should be unique
                                to that particular script tag.
            callbackFunction    An optional function to execute when the script is
                                found.  Use null if not needed.
    */
    if ( ! controlArray.length) return null;

    checkForBadJavascripts      = function (zEvent) {

        for (var J = controlArray.length - 1;  J >= 0;  --J) {
            var bSearchSrcAttr      = controlArray[J][0];
            var identifyingRegex    = controlArray[J][1];

            if (bSearchSrcAttr) {
                if (identifyingRegex.test (zEvent.target.src) ) {
                    stopBadJavascript (J);
                    return false;
                }
            }
            else {
                if (identifyingRegex.test (zEvent.target.textContent) ) {
                    stopBadJavascript (J);
                    return false;
                }
            }
        }

        function stopBadJavascript (controlIndex) {
            zEvent.stopPropagation ();
            zEvent.preventDefault ();

            var callbackFunction    = controlArray[J][2];
            if (typeof callbackFunction == "function")
                callbackFunction ();

            //--- Remove the node just to clear clutter from Firebug inspection.
            zEvent.target.parentNode.removeChild (zEvent.target);

            //--- Script is intercepted, remove it from the list.
            controlArray.splice (J, 1);
            if ( ! controlArray.length) {
                //--- All done, remove the listener.
                window.removeEventListener (
                    'beforescriptexecute', checkForBadJavascripts, true
                );
            }
        }
    }

    /*--- Use the "beforescriptexecute" event to monitor scipts as they are loaded.
        See https://developer.mozilla.org/en/DOM/element.onbeforescriptexecute
        Note that it does not work on acripts that are dynamically created.
    */
    window.addEventListener ('beforescriptexecute', checkForBadJavascripts, true);

    return checkForBadJavascripts;
}

function addJS_Node (text, s_URL, funcToRun) {
    var D                                   = document;
    var scriptNode                          = D.createElement ('script');
    scriptNode.type                         = "text/javascript";
    if (text)       scriptNode.textContent  = text;
    if (s_URL)      scriptNode.src          = s_URL;
    if (funcToRun)  scriptNode.textContent  = '(' + funcToRun.toString() + ')()';

    var targ = D.getElementsByTagName ('head')[0] || D.body || D.documentElement;
    //--- Don't error check here. if DOM not available, should throw error.
    targ.appendChild (scriptNode);
}
于 2012-05-06T05:39:35.287 回答
-1

以下 Greasemonkey 用户脚本（基于此源）终于为我工作了。script它通过在现有标记之后的新标记中定义另一个具有相同名称的函数来覆盖现有函数script。没有@run-at或beforescriptexecute需要。

var firstScript = document.body.getElementsByTagName('script')[0];
var newScript = document.createElement('script');
var scriptArray = new Array();
scriptArray.push('function init() {');
scriptArray.push('    ...');
scriptArray.push('}');
newScript.innerHTML = scriptArray.join('\n');
scriptArray.length = 0; // free this memory
firstScript.parentNode.insertBefore(newScript, firstScript.nextSibling);

我以前没有太多使用 Greasemonkey 甚至 Javascript 的经验，所以我发现 Firefox Web Developer 工具必不可少，特别是：

  • 错误控制台以捕获您一定会犯的许多小错误。和
  • 检查工具以查看生成的 HTML（因为常规查看源代码没有显示！）。
于 2012-05-07T15:53:24.560 回答