How to removeEventListener that is addEventListener with anonymous function?

问题

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. \');

回答1:

You can't. You have to use a named function or store the reference somehow.

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);

The best would be to do this in a structured way, so that you can identify different handlers and remove them. In the example above, you obviously could only remove the last handler.

Update:

You could create your own handler handler (:)) :

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];
            }
        }
    };
}());

Then you can use it with:

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

回答2:

You can't, you need a reference to the function:

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. ');

回答3:

You could also do this like that:

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

Then you can remove the event listener like this:

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

// Remove event listener
disposer();

回答4:

if you dont have to support IE, you can use the once option

[Element].addEventListener('click', () => {...}, {
  capture: false,
  once: true
});

来源：https://stackoverflow.com/questions/5660131/how-to-removeeventlistener-that-is-addeventlistener-with-anonymous-function

标签

javascript

event-handling

anonymous-function