Coffeescript理解和封闭问题

Question

将一些JavaScript转换为CoffeeScript时遇到了问题.基本问题是我从使用$ .each到CoffeeScript理解,现在我遇到了一个问题,即闭包中捕获了理解的最后一个值.让我们从原始JavaScript开始:

function bindKeyboardControls(websocket) {
    var moveKeyMap = {
        Down: ['down', 's'],
        Up: ['up', 'w'],
        Left: ['left', 'a'],
        Right: ['right', 'd']
    };

    $.each(moveKeyMap, function (direction, keys) {
        $.each(keys, function (_, key) {
            $(document).bind('keydown', key, function () { move(websocket, direction); });
        });
    });
};

这是我第一次尝试使用CoffeeScript:

    bindKeyboardControls = (websocket) ->
    moveKeyMap =
        Down: ['down', 's']
        Up: ['up', 'w']
        Left: ['left', 'a']
        Right: ['right', 'd']        
    for direction, keys of moveKeyMap
        for key in keys
            $(document).bind('keydown', key, -> move(websocket, direction))
    null

为什么这不起作用？那么这里是生成的JavaScript:

bindKeyboardControls = function(websocket) {
  var direction, key, keys, moveKeyMap, _i, _len;
  moveKeyMap = {
    Down: ['down', 's'],
    Up: ['up', 'w'],
    Left: ['left', 'a'],
    Right: ['right', 'd']
  };
  for (direction in moveKeyMap) {
    keys = moveKeyMap[direction];
    for (_i = 0, _len = keys.length; _i < _len; _i++) {
      key = keys[_i];
      $(document).bind('keydown', key, function() {
        return move(websocket, direction);
      });
    }
  }
  return null;
};

你看到在函数的顶部如何声明'direction'变量？传递给document.bind的函数是在该变量上创建一个闭包,因此在函数运行时,direction始终等于最后一个值('Right').

这是一个有点难看的固定版本:

    bindKeyboardControls = (websocket) ->
    moveKeyMap =
        Down: ['down', 's']
        Up: ['up', 'w']
        Left: ['left', 'a']
        Right: ['right', 'd']        
    for direction, keys of moveKeyMap
        for key in keys                             
            ((d) -> $(document).bind('keydown', key, -> move(websocket, d)))(direction)
    null        

我也可以回去使用$ .each.所以我确实有一些解决方案,但有更好的解决方案吗？

Answer 1

是:

for direction, keys of moveKeyMap
  for key in keys
    do (direction, key) -> $(document).bind('keydown', key, -> move(websocket, d))

创建和运行捕获的值的匿名函数direction和key,这样的bind回调可以使用它们.有关详细信息,请参阅我的PragProg文章A CoffeeScript干预.