Agario Movement Keys

// ==UserScript==
// @name         Agario Movement Keys
// @description  Use arrow keys or WASD to move. E to eject mass.
// @version      0.4
// @match        http://agar.io/
// @grant        none
// @noframes
// ==/UserScript==

(function overwriteCanvasLoop() {
    'use strict';

    var canvas = document.getElementById('canvas');
    if (!canvas || !canvas.onmousemove) {
        setTimeout(overwriteCanvasLoop, 100);
        return;
    }

    var endPoint = {
        clientX: window.innerWidth / 2,
        clientY: window.innerHeight / 2
    };

    var handleKeys = (function() {
        var keys = [ 37, 38, 39, 40, 65, 87, 68, 83 ];
        var key = {
            left: 'keyup',
            up: 'keyup',
            right: 'keyup',
            down: 'keyup'
        };
        ['blur', 'resize'].forEach(function(listener) {
            window.addEventListener(listener, function() {
                key.left = key.up = key.right = key.down = 'keyup';
                endPoint = {
                    clientX: window.innerWidth / 2,
                    clientY: window.innerHeight / 2
                };
            }, false);
        });
        return function(event, keyState) {
            if (event.repeat && keyState === 'keydown') {
                return;
            }
            for (var i = 0; i < keys.length; i++) {
                if (event.which !== keys[i]) continue;
                var axis = (i % 2) ? {
                    dir: [ 'up', 'down' ],
                    value: 'clientY'
                } : {
                    dir: [ 'left', 'right' ],
                    value: 'clientX'
                };
                var direction = ((i % 4) === 0 || ((i - 1) % 4) === 0) ? axis.dir[0] : axis.dir[1];
                if (key[direction] === keyState) {
                    return;
                }
                key[direction] = keyState;
                var point = (keyState === 'keydown') ? 500 : -500;
                point = (direction === 'left' || direction === 'up') ? -point : point;
                return [ axis.value, point ];
            }
        };
    })();

    ['keydown', 'keyup'].forEach(function(keyState) {
        window.addEventListener(keyState, function(event) {
            var data = handleKeys(event, keyState);
            if (data && keyState === 'keyup') {
                var fraction = data[1] / 10;
                for (var i = 0; i < 2; i++) {
                    endPoint[data[0]] += (fraction * (i ? 1 : 9));
                    canvas.onmousemove(endPoint);
                }
            } else if (data && keyState === 'keydown') {
                endPoint[data[0]] += data[1];
                canvas.onmousemove(endPoint);
            }
            if (event.which === 87) {
                event.stopPropagation();
            } else if (event.which === 69) {
                window['on' + keyState]({ keyCode: 87 });
            }
        }, true);
    });
})();