如何使用匿名函数removeEventListener作为addEventListener？

Question

function doSomethingWith(param)
{
    document.body.addEventListener(
        'scroll',
        function()
        {
            document.write(param);
        },
        false
    ); // An event that I want to remove later
}
setTimeout(
    function()
    {
        document.body.removeEventListener('scroll', HANDLER ,false);
            // What HANDLER should I specify to remove the anonymous handler above?
    },
    3000
);
doSomethingWith('Test. ');

Answer 1

你不能.您必须使用命名函数或以某种方式存储引用.

var handler;

function doSomethingWith(param) {
    handler = function(){
        document.write(param);
    };  
    document.body.addEventListener('scroll', handler,false);
}
setTimeout(function() {
     document.body.removeEventListener('scroll', handler ,false);
}, 3000);

最好的方法是以结构化的方式执行此操作,以便您可以识别不同的处理程序并将其删除.在上面的示例中,您显然只能删除最后一个处理程序.

更新:

您可以创建自己的处理程序处理程序(:)):

var Handler = (function(){
    var i = 1,
        listeners = {};

    return {
        addListener: function(element, event, handler, capture) {
            element.addEventListener(event, handler, capture);
            listeners[i] = {element: element, 
                             event: event, 
                             handler: handler, 
                             capture: capture};
            return i++;
        },
        removeListener: function(id) {
            if(id in listeners) {
                var h = listeners[id];
                h.element.removeEventListener(h.event, h.handler, h.capture);
                delete listeners[id];
            }
        }
    };
}());

然后你可以用它:

function doSomethingWith(param) {
    return Handler.addListener(document.body, 'scroll', function() {
        document.write(param);
    }, false);
}

var handler = doSomethingWith('Test. ');

setTimeout(function() {
     Handler.removeListener(handler);
}, 3000);

DEMO

Answer 2

你不能,你需要一个参考功能:

function doSomethingWith(param) {
   var fn = function(){ document.write(param); };
   document.body.addEventListener('scroll', fn, false);
   setTimeout(function(){ document.body.removeEventListener('scroll', fn, false); }, 3000);
}
doSomethingWith('Test. ');

Answer 3

您也可以这样做：

const ownAddEventListener = (scope, type, handler, capture) => {
  scope.addEventListener(type, handler, capture);
  return () => {
    scope.removeEventListener(type, handler, capture);    
  }
}

然后，您可以像这样删除事件监听器：

// Add event listener
const disposer = ownAddEventListener(document.body, 'scroll', () => { 
  // do something
}, false);

// Remove event listener
disposer();