Remove a javascript function with Greasemonkey

Question

I visit a website with a javascript file in the head of the HTML

Answer 1

It's not clear that update is a global function. If it isn't then that approach won't work.

But you can override the keypress handler with:

unsafeWindow.document.onkeypress = function(){};

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For a general, high-powered way to selectively block, or replace, any JS (on Firefox), use @run-at document-start and the checkForBadJavascripts function, like so:

// ==UserScript==
// @name        _Replace select javascript on a page
// @include     http://YOUR_SERVER.COM/YOUR_PATH/*
// @require     https://gist.github.com/raw/2620135/checkForBadJavascripts.js
// @run-at      document-start
// @grant       GM_addStyle
// ==/UserScript==
/*- The @grant directive is needed to work around a design change
    introduced in GM 1.0.   It restores the sandbox.
*/

checkForBadJavascripts ( [
    [   false,
        /document\.onkeypress\s*=\s*update/,
        function () {
            addJS_Node (myKeypressFunction.toString() );
            addJS_Node ('document.onkeypress = myKeypressFunction;');
        }
    ]
] );


function myKeypressFunction (evt) {
    /*  DO WHATEVER HERE BUT USE NO GREASEMONKEY FUNCTIONS INSIDE
        THIS FUNCTION.
    */
    console.log ("Keypress function fired.");
}

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See this answer, for more information on checkForBadJavascripts.