我该如何发射移动的子弹？

Question

Hi I'm new here and also in the programming world, so, I have a little problem: I'm making a simple game engine in JS because I want to replicate the original Space Invaders game, the problem is just the bullet is not moving, only appears and disappears, like a laser shot. I want to have a moving bullet. Anyone can help me? PS I don't wanna use object oriented programming here, I want to make the whole game in a single .js file.

console.log('GAME LOADED//SPACE INVADERS');

////////////////////////////////////////////////

let screen = document.createElement('canvas');
screen.width = 800;
screen.height = 900;
document.body.appendChild(screen);
document.addEventListener('keydown', keyDown, false);
document.addEventListener('keyup', keyUp, false);
let ctx = screen.getContext('2d');

////////////////////////////////////////////////

let x = screen.width / 2;
let y = screen.height / 2;
let bulletY = screen.height - 20;
let bulletSpeed = 10;
let bulletLifeTime = 3;
let size = 20;
let sWidth = screen.width;
let sHeight = screen.height;
let columns = screen.width / size;
let rows = screen.height / size;
let speed = 5;
let right = false;
let left = false;
let up = false;
let down = false;
let shot = false;
let gravity = 10;
let jumpForce = 40 ;

/////////////////////////////////////////////////

function keyDown() {
    switch(event.keyCode) {
        case 39: right = true;
                 break;
        case 37: left = true;
                 break;
        //case 40: up = true;
                 //break;
        //case 38: down = true;
                 //break;
        case 32: shot = true;  
                 break;        
    }
}

function keyUp() {
    switch(event.keyCode) {
        case 39: right = false;
                 break;
        case 37: left = false;
                 break;
        //case 40: up = false;
                 //break;
        //case 38: down = false;
                 //break;
        case 32: shot = false; 
                 break;        
    }
}

function move() {
    if(right == true) {
        x += 1 * speed;
    } else if(left == true) {
        x -= 1 * speed;
    }
    //if(up == true) {
        //y += 1 * speed;
    //} else if(down == true) {
        //y -= 1 * speed;
    //}
}

 function player() {
    ctx.fillStyle = '#1CE80D';
    ctx.fillRect(x, y, size, size);
    ctx.fillRect(x+10, y, size, size);
    ctx.fillRect(x+20, y, size, size);
    ctx.fillRect(x-10, y, size, size);
    ctx.fillRect(x-20, y, size, size);
    ctx.fillRect(x+5, y-1, 10, 10);
    ctx.fillRect(x+5, y-2, 10, 10);
    ctx.fillRect(x+5, y-3, 10, 10);
    ctx.fillRect(x+5, y-4, 10, 10);
    ctx.fillRect(x+5, y-5, 10, 10);
    ctx.fillRect(x+5, y-6, 10, 10);
    ctx.fillRect(x+5, y-7, 10, 10);
    ctx.fillRect(x+9, y-8, 2, 2);
    ctx.fillRect(x+9, y-9, 2, 2);
    ctx.fillRect(x+9, y-10, 2, 2);
    ctx.fillStyle = 'black';
    ctx.fillRect(x+35, y, 5, 5);
    ctx.fillRect(x-20, y, 5, 5);
}

function enemy1() {
    ctx.fillStyle = '#1CE80D';
    ctx.fillRect(444, 375, 5, 5);
    ctx.fillRect(411, 375, 5, 5);
    ctx.fillRect(416, 380, 5, 5);
    ctx.fillRect(439, 380, 5, 5);
    ctx.fillRect(410, 385, 40, 5);
    ctx.fillRect(405, 390, 50, 5);
    ctx.fillRect(400, 395, 60, 5);
    ctx.fillRect(400, 400, 60, 5);
    ctx.fillRect(400, 405, 5, 5);
    ctx.fillRect(455, 405, 5, 5);
    ctx.fillRect(410, 405, 40, 5);
    ctx.fillStyle = '#001119';
    ctx.fillRect(415, 405, 30, 5);
    ctx.fillStyle = '#1CE80D';
    ctx.fillRect(415, 410, 30, 5);
    ctx.fillStyle = '#001119';
    ctx.fillRect(440, 390, 5, 5);
    ctx.fillRect(414, 390, 5, 5);
    ctx.fillRect(428, 410, 4, 5);  
}

function draw() {
    ctx.fillStyle = '#001119';
    let background = ctx.fillRect(0, 0, sWidth, sHeight);
    player();

    ctx.fillStyle = '#EAEEB7';
    let wall1 = ctx.fillRect(0, 0, 10, sHeight);
    let wall2 = ctx.fillRect(0, 0, sHeight, 10);
    let wall3 = ctx.fillRect(0, sHeight - 10, sWidth, 10);
    let wall4 = ctx.fillRect(sWidth - 10, 0, 10, sHeight);
}

function gravityForce() {
    y += gravity;
}

function jumpAct() {
    if(jump == true) {
        y -= jumpForce;
    } else if(jump == false) {
        gravityForce();
   }
}

function bulletDraw() {
    let bulletX = x;
    ctx.fillStyle = '#1CE80D';
    ctx.fillRect(bulletX + 9, bulletY, 1, 8);
}

function bulletPos() {
    bulletY -= bulletSpeed;    
}

function attack() {
    if(shot == true) {
        for(let i = screen.height; i > 0; i--) {
        bulletDraw();
        bulletPos();
        }
        console.log('shooting');
    } else if(shot == false) {
        bulletY = 880;
    }
}

function gameLoop() {
    ctx.clearRect(0, 0, screen.width, screen.height);
    draw();
    move(); 
    gravityForce();
    attack(); 
    enemy1();
    bulletPos();
    requestAnimationFrame(gameLoop); 
    if(x > screen.width - size - 30) {
        x = 30
    } else if(x < 30) {
        x = screen.width - 50;
    }
    if(y > screen.height - size - 10) {
        y -= (size - 10);
    } else if(y < 0) {
        y += size;
    } 
}
////////////////////////////////////////////////

requestAnimationFrame(gameLoop);

Answer 1

I think you have to manage both timer interval and canvas redraw function. I don't thing it is a good idea to redraw the entire canvas in each interval, instead you can redraw only the required canvas area. I have modified your code with setTimeout() function without redraw the entire canvas. You can see the complete code in this fiddler path https://jsfiddle.net/SyamKumarD/knyt7shf/18/

Some of the key code you need to check

1. setTimeout() method
2. hitTarget() method and its instantiation
3. Key down and up events

Hope this will helps