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134
ViewsPlayer Speeding Up In JavaScript Game
Every single time I move with the right or left arrows keys or A or D, the player speeds up. I don't want this to happen. I want the player to move at the same speed whenever you press the move key. I have no idea why this is happening. Here is my code:
class Player {
constructor(x, y, color, width, height, health, strength, type, speed) {
this.x = x;
this.y = y;
this.color = color;
this.width = width;
this.height = height;
this.health = health;
this.strength = strength;
this.type = type;
this.speed = speed;
}
draw() {
c.beginPath();
c.rect(this.x, this.y, this.width, this.height);
c.fillStyle = this.color;
c.fill();
c.stroke();
}
moveLeft(){
this.x -= this.speed;
}
moveRight(){
this.x += this.speed;
}
moveUp(){
this.y += this.speed;
}
}
var x = canvas.width / 2;
var y = canvas.height / 2;
var left = false;
var up = false;
var right = false;
var left2 = false;
var up2 = false;
var right2 = false;
var pressing;
var player = new Player(x, y, 'red', 30, 30, 100, 30, 'basic', 2);
player.draw();
document.addEventListener('keydown', function(e) {
switch (e.keyCode) {
case 37:
left = true;
setInterval(function pressing(){
if(left2===false && left === true){
player.moveLeft();
}
},10)
break;
case 65:
left2 = true;
setInterval(function pressing(){
if(left===false && left2 === true){
player.moveLeft();
}
},10)
break;
case 39:
right = true;
setInterval(function pressing(){
if(right2===false && right === true){
player.moveRight();
}
},10)
break;
case 68:
right2 = true;
setInterval(function pressing(){
if(right===false && right2 === true){
player.moveRight();
}
},10)
break;
}
});
document.addEventListener("keyup", event => {
clearInterval(pressing);
if (event.keyCode === 37) {
left = false;
}
if (event.keyCode === 65) {
left2 = false;
}
if (event.keyCode === 39) {
right = false;
}
if (event.keyCode === 68) {
right2 = false;
}
});
I followed many tutorials but couldn't find a different easy way to move my player. Does anyone have another strategy for moving or know why this isn't working?
2 answers
Answer question0
On every keypress you are currently creating a new interval that is never stopped. So what you are actually doing is to create duplicate intervals each time the key is pressed. As a first, rough fix you could try to store the return value of setInterval in a variable outside of the scope of the key event handler and check whether you have earlier intervals running. If so, clear them up before going ahead.
As clearInterval does not throw any error when fed un-intervalish values, you don't even have to check before clearing:
let myInterval = null
document.addEventListener('keydown', (e) => {
// Clean up any earlier mess.
clearInterval(myInterval)
// Create new mess.
myInterval = setInterval(() => { /* do something */ }, 10)
})
0
I think that you already have the answer...
You are creating multiple intervals that are never stopped.
But I would not use the interval in the key events, instead use just one outside to draw at certain frequency, then use a more mathematical approach to move and set the speed of the player on those events, we don't need different functions to move left or right, all we need is the correct speed value, positive increases (moves right), negative decreases (moves left) ... here is the code:
class Player {
constructor(pos, speed) {
this.pos = pos
this.speed = speed
}
draw() {
this.pos.x += this.speed.x
this.pos.y += this.speed.y
c.clearRect(0, 0, canvas.width, canvas.height)
c.beginPath()
c.rect(this.pos.x, this.pos.y, 20, 20)
c.fill()
}
}
let canvas = document.getElementById("game")
let c = canvas.getContext("2d")
var player = new Player({ x: 60, y: 50 }, { x: 0, y: 0 })
setInterval(() => player.draw(), 50)
document.addEventListener("keydown", function (e) {
switch (e.keyCode) {
case 37:
case 65:
player.speed.x = -1
break
case 39:
case 68:
player.speed.x = 1
break
}
})
document.addEventListener("keyup", function (e) {
switch (e.keyCode) {
case 37:
case 65:
case 39:
case 68:
player.speed.x = 0
break
}
})<canvas id="game"></canvas>I did simplify a lot of your code to keep this example small...
If you are really serious about building a JS game you should look at some of the game engines:
https://github.com/collections/javascript-game-engines
Those are some of the most popular open source ones