document.onkeydown = function(e) {
var key = e.keyCode;
if (key===37) {//left arrow pressed
} else if (key===39) {//right arrow pressed
}
}
javascript keypress to control animation
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14-10-2022 - |
Question
Space Invader game: I want to control the 'base gun' (move it left and right and fire missiles at the invaders. So I need a keypress or (keydown?) event to change a variable (x coordinate) and a key press event to fire a missile.
Can anyone show me how the keypress event is detected and the variable is changed?
La solution
Autres conseils
Like this?
document.onkeydown = checkKey;
var xCoord = 100;
function checkKey(e) {
e = e || window.event;
switch (e.keyCode) {
case 37 : // left
xCoord -= 5;
break;
case 39 : // right
xCoord += 5;
break;
}
}
Exciting fiddle: http://jsfiddle.net/u5eJp/
Couple things I would like to add to the other answers:
1) Use constants to make it easier on yourself
2) There is no way to check if a key is currently pressed in javascript, so you should keep track of what is currently pressed as well
var pressed = {
up: false,
down: false,
left: false,
right: false
};
var LEFT_ARROW = 37;
var UP_ARROW = 38;
var RIGHT_ARROW = 39;
var DOWN_ARROW = 40;
document.onkeydown = function (e) {
e = e || window.event;
switch (e.keyCode) {
case LEFT_ARROW:
pressed.left = true;
break;
case UP_ARROW:
pressed.up = true;
break;
case RIGHT_ARROW:
pressed.right = true;
break;
case DOWN_ARROW:
pressed.down = true;
break;
default:
break;
}
}
//update position separately
function updatePos() {
if (pressed.up) { //change y up }
if (pressed.down) { //change y down }
if (pressed.left) { //change x left }
if (pressed.right) { //change x right }
}
Hope this helps, and good luck!
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