javascript - 使用removeEventListener删除包装函数回调

Question

我有这段代码，它可以通过单击并拖动在 Canvas 上拖动一个球。

canvas.addEventListener('mousedown', function () {
  var initialClickX = mouse.x;
  var initialClickY = mouse.y;
  var initialBallX = ball.x;
  var initialBallY = ball.y;

  canvas.addEventListener('mousemove', function() {
      onMouseMove(initialClickX, initialClickY, mouse.x, mouse.y, initialBallX, initialBallY)
  }, false);

}, false);

function onMouseMove(initialClickX, initialClickY, mouseX, mouseY, initialBallX,     initialBallY){
    ball.x = mouseX + initialBallX - initialClickX;
    ball.y = mouseY + initialBallY - initialClickY;
    draw();
}

问题是，当我松开鼠标时，我无法让球停止拖动。我知道我需要添加:

    canvas.removeEventListener('mousemove', function() {
      onMouseMove(initialClickX, initialClickY, mouse.x, mouse.y, initialBallX, initialBallY)
  }, false);

但是因为该函数位于包装器中，所以上面的内容没有任何效果，并且球仍然粘在我的光标上。谁能建议解决这个问题的方法吗？

Answer 1

不要使用匿名函数。您需要保存对事件监听器函数的引用以便稍后删除。

canvas.addEventListener('mousedown', function () {
  var initialClickX = mouse.x;
  var initialClickY = mouse.y;
  var initialBallX = ball.x;
  var initialBallY = ball.y;

  function wrapper() {
      onMouseMove(initialClickX, initialClickY, mouse.x, mouse.y, initialBallX, initialBallY)
  }

  canvas.addEventListener('mousemove', wrapper, false);

  // some time later
  canvas.removeEventListener('mousemove', wrapper);

}, false);