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I want to stop the execution of one single line from a site, so that the whole page is read by the browser except that single line. Or the browser may simply skip the execution of that javascript function.
OR
Is there way i can tweak the javascript somehow so that the random number generating function in javascript do not generate random number, but the numbers i want...
I dont have access to the site on which the script is hosted so all this needs to be done client side.
988
When you click Call the function button, it will execute the function. To stop the function, click Stop the function execution button.
The break statement can use a label reference, to break out of any JavaScript code block (see "More Examples" below).
Window stop() The stop() method is the same as clicking stop in the browser.
Firefox currently supports the beforescriptexecute event (as of Version 4, released on March 22, 2011)‡.
With that event and the // @run-at document-start directive, Firefox and Greasemonkey now seem to do a good job intercepting specific <script> tags.
This is still not possible for Chrome+Tampermonkey. For anything but Firefox+Greasemonkey, you will need to use techniques as shown in the other answers, below, of write a full browser extension.
The checkForBadJavascripts function encapsulates this. For example, suppose the page had a <script> tag like so:
<script> alert ("Sorry, Sucka! You've got no money left."); </script> You could use checkForBadJavascripts like so:
checkForBadJavascripts ( [ [ false, /Sorry, Sucka/, function () { addJS_Node ('alert ("Hooray, you\'re a millionaire.");'); } ] ] ); to get a much nicer message. (^_^)
See the inline documentation, in checkForBadJavascripts, for more.
To see a demonstration in a complete script, first visit this page at jsBin. You will see 3 lines of text, two of them added by JS.
Now, install this script (View source; it's also below.) and revisit the page. You will see that the GM-script deleted one bad tag and replaced another with our "good" JS.
‡ Note that only Firefox supports the beforescriptexecute event. And it was removed from the HTML5 spec with no equivalent capability specified.
Complete GM script example (The same as the one at GitHub and jsBin):
Given this HTML:
<body onload="init()"> <script type="text/javascript" src="http://jsbin.com/evilExternalJS/js"></script> <script type="text/javascript" language="javascript"> function init () { var newParagraph = document.createElement ('p'); newParagraph.textContent = "I was added by the old, evil init() function!"; document.body.appendChild (newParagraph); } </script> <p>I'm some initial text.</p> </body>
Use this Greasemonkey script:
// ==UserScript== // @name _Replace evil Javascript // @include http://jsbin.com/ogudon* // @run-at document-start // ==/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); } If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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