events - Javascript Key Handler -

i have javascript key handler function , im trying use in game im working out doesnt seem quite working , im not sure if editor or code has errors. code shown:

var mykey = {     pressedkeys: [],     left: 37,     up: 38,     right: 39,     down: 40,     ispressed: function(zkey){         return this.pressedkeys[zkey];     },     onkeydown: function(event){         this.pressedkeys[event.keycode] = true;     },     onkeyup: function(event){         this.pressedkeys[event.keycode] = false;        }, };  window.addeventlistener("keydown", mykey.onkeydown); window.addeventlistener("keyup", mykey.onkeyup);  var checkinput = function(){     if(mykey.pressedkeys[mykey.left]){         confirm("pressed left");     } }  var gameloop = function(){     checkinput();     window.requestanimationframe(gameloop); } 

the game loop animation frame called first time in main function thats not shown here. dont understand going wrong. tried hard coding numbers , still nothing editor.

when reference method , use event handler, function no longer associated object. this inside function not reference mykey object, reference window object (as object event happens).

you can use bind method specify context functions:

window.addeventlistener("keydown", mykey.onkeydown.bind(mykey)); window.addeventlistener("keyup", mykey.onkeyup.bind(mykey)); 

note bind method not supported in older browsers, example ie8 , older, need 'polyfill' if need support them. there 1 in documentation linked above.

you can use function wrapper call methods:

window.addeventlistener("keydown", function(e){ mykey.onkeydown(e); }); window.addeventlistener("keyup", function(e){ mykey.onkeyup(e); });