JavaScript move delay and multiple keystrokes

javascript, keycode

Solution

First, to avoid the keypress/repeat delay, you have to wrap your program in a loop, and make the state of the keyboard available inside the scope of that loop, secondly to monitor multiple keypresses you need to keep track of individual keydown and keyup events:

var x = 0;
var y = 0;

// store the current pressed keys in an array
var keys = [];

// if the pressed key is 38 (w) then keys[38] will be true
// keys [38] will remain true untill the key is released (below)
// the same is true for any other key, we can now detect multiple
// keypresses
$(document).keydown(function (e) {
    keys[e.keyCode] = true;
});

$(document).keyup(function (e) {
    delete keys[e.keyCode];
});
// we use this function to call our mainLoop function every 200ms
// so we are not relying on the key events to move our square
setInterval( mainLoop , 200 );

function mainLoop() {
     // here we query the array for each keyCode and execute the required actions
     if(keys[37]){
        x -= 10;
        $("#square").css("left", x);
     }

     if(keys[39]){
        x += 10;
        $("#square").css("left", x);
     }

     if(keys[38]){
        y -= 10;
        $("#square").css("top", y);
     }

     if(keys[40]){
        y += 10;
        $("#square").css("top", y);
     }
}

Problem

Original source