如何使用currying函数删除事件侦听器

Question

I'm having a hard time to remove Event listener type currying function.

// I register first, at some time I want to remove using freezeHighlight but it doesn't working (without currying function it's working like a charm)
const privateMethods = {
  highlighted (index) {
    return function (event) {
      event.target.setAttribute('filter', 'url(#glow)')

      // need param index later
    }
  }
}

register (node, index) {
      node.addEventListener('mouseover', privateMethods.highlighted(index))
  }

freezeHighlight (node) {
        node.removeEventListener('mouseover', privateMethods.highlighted)
  }

Is it possible to remove event listener type currying function or should I procede with a workaround?

Answer 1

You need to memoize the handler you create so that you can remove it later.

const handlers = {};

const privateMethods = {
  highlighted (index) {
    // return the saved handler if we've been called before
    // or create a new handler, save it, and return it.
    return handlers[index] || (handlers[index] = function (event) {
      event.target.setAttribute('filter', 'url(#glow)')

      // need param index later
    });
  }
}

register (node, index) {
      // add the handler
      node.addEventListener('mouseover', privateMethods.highlighted(index))
}

freezeHighlight (node, index) {
      // will remove the handler
        node.removeEventListener('mouseover', privateMethods.highlighted(index))
}

Answer 2

var listener
register (node, index) {
    listener = privateMethods.highlighted(index)
    node.addEventListener('mouseover', )
}

freezeHighlight (node) {
    node.removeEventListener('mouseover', listener)
}

You think privateMethods.highlighted is the listener. No it's not. The return value of privateMethods.highlighted(index) is the listener.