js实现点击烟花特效

代码：

<script type=\"text/javascript\">
function clickEffect() {
  let balls = [];
  let longPressed = false;
  let longPress;
  let multiplier = 0;
  let width, height;
  let origin;
  let normal;
  let ctx;
  const colours = [\"#F73859\", \"#14FFEC\", \"#00E0FF\", \"#FF99FE\", \"#FAF15D\"];
  const canvas = document.createElement(\"canvas\");
  document.body.appendChild(canvas);
  canvas.setAttribute(\"style\", \"width: 100%; height: 100%; top: 0; left: 0; z-index: 99999; position: fixed; pointer-events: none;\");
  const pointer = document.createElement(\"span\");
  pointer.classList.add(\"pointer\");
  document.body.appendChild(pointer);

  if (canvas.getContext && window.addEventListener) {
    ctx = canvas.getContext(\"2d\");
    updateSize();
    window.addEventListener(\'resize\', updateSize, false);
    loop();
    window.addEventListener(\"mousedown\", function(e) {
      pushBalls(randBetween(10, 20), e.clientX, e.clientY);
      document.body.classList.add(\"is-pressed\");
      longPress = setTimeout(function() {
        document.body.classList.add(\"is-longpress\");
        longPressed = true;
      }, 500);
    }, false);
    window.addEventListener(\"mouseup\", function(e) {
      clearInterval(longPress);
      if (longPressed == true) {
        document.body.classList.remove(\"is-longpress\");
        pushBalls(randBetween(50 + Math.ceil(multiplier), 100 + Math.ceil(multiplier)), e.clientX, e.clientY);
        longPressed = false;
      }
      document.body.classList.remove(\"is-pressed\");
    }, false);
    window.addEventListener(\"mousemove\", function(e) {
      let x = e.clientX;
      let y = e.clientY;
      pointer.style.top = y + \"px\";
      pointer.style.left = x + \"px\";
    }, false);
  } else {
    console.log(\"canvas or addEventListener is unsupported!\");
  }


  function updateSize() {
    canvas.width = window.innerWidth * 2;
    canvas.height = window.innerHeight * 2;
    canvas.style.width = window.innerWidth + \'px\';
    canvas.style.height = window.innerHeight + \'px\';
    ctx.scale(2, 2);
    width = (canvas.width = window.innerWidth);
    height = (canvas.height = window.innerHeight);
    origin = {
      x: width / 2,
      y: height / 2
    };
    normal = {
      x: width / 2,
      y: height / 2
    };
  }
  class Ball {
    constructor(x = origin.x, y = origin.y) {
      this.x = x;
      this.y = y;
      this.angle = Math.PI * 2 * Math.random();
      if (longPressed == true) {
        this.multiplier = randBetween(14 + multiplier, 15 + multiplier);
      } else {
        this.multiplier = randBetween(6, 12);
      }
      this.vx = (this.multiplier + Math.random() * 0.5) * Math.cos(this.angle);
      this.vy = (this.multiplier + Math.random() * 0.5) * Math.sin(this.angle);
      this.r = randBetween(8, 12) + 3 * Math.random();
      this.color = colours[Math.floor(Math.random() * colours.length)];
    }
    update() {
      this.x += this.vx - normal.x;
      this.y += this.vy - normal.y;
      normal.x = -2 / window.innerWidth * Math.sin(this.angle);
      normal.y = -2 / window.innerHeight * Math.cos(this.angle);
      this.r -= 0.3;
      this.vx *= 0.9;
      this.vy *= 0.9;
    }
  }

  function pushBalls(count = 1, x = origin.x, y = origin.y) {
    for (let i = 0; i < count; i++) {
      balls.push(new Ball(x, y));
    }
  }

  function randBetween(min, max) {
    return Math.floor(Math.random() * max) + min;
  }

  function loop() {
    ctx.fillStyle = \"rgba(255, 255, 255, 0)\";
    ctx.clearRect(0, 0, canvas.width, canvas.height);
    for (let i = 0; i < balls.length; i++) {
      let b = balls[i];
      if (b.r < 0) continue;
      ctx.fillStyle = b.color;
      ctx.beginPath();
      ctx.arc(b.x, b.y, b.r, 0, Math.PI * 2, false);
      ctx.fill();
      b.update();
    }
    if (longPressed == true) {
      multiplier += 0.2;
    } else if (!longPressed && multiplier >= 0) {
      multiplier -= 0.4;
    }
    removeBall();
    requestAnimationFrame(loop);
  }

  function removeBall() {
    for (let i = 0; i < balls.length; i++) {
      let b = balls[i];
      if (b.x + b.r < 0 || b.x - b.r > width || b.y + b.r < 0 || b.y - b.r > height || b.r < 0) {
        balls.splice(i, 1);
      }
    }
  }
}
clickEffect();//调用
</script>

效果：

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