How to change the value on a input in someone else page?

Question

<div class="xCoord">
    <label for="xCoordInput">X:</label>
    <input value="" name="x" id="xCoordInput" class="text coordinates x ">
</div>

What I would like to do is to change this value ( xCoordInput ) on someone else website? This is a game and I don't know how I would change their website from my own website.

Answer 1

I like to autofill forms with a bookmarklet . I use them at work to fill out tedious forms when I am testing webpages. To build one create a bookmark and edit the url value of the bookmark to hold a javascript function object like this one.

javascript:(function(){ 
    var xCoord = document.getElementsByClassName("xCoord")[0];
    xCoord.getElementsByTagName("input")[0].value="whatever";  
})();

Nothing about doing this in principle is wrong or illegal unless you are using it to cheat or break the law.