javascript – 删除使用bind(this)添加的事件侦听器

如何在下面的构造函数中删除绑定到窗口的单击侦听器？我需要它来监听窗口,我需要访问其中的按钮实例.

class MyEl extends HTMLButtonElement {
  constructor() {
    super();
    this.clickCount = 0;
    window.addEventListener('click', this.clickHandler.bind(this));
  }
  
  clickHandler(e) {
    if (e.target === this) {
      this.textContent = `clicked ${++this.clickCount} times`;
      window.removeEventListener('click', this.clickHandler);
    }
  }
  
  disconnectedCallback() {
      window.removeEventListener('click', this.clickHandler);
  }
}

customElements.define('my-el', MyEl, { extends: 'button' });

<button is="my-el" type="button">Click me</button>

解决方法:

你当前的实现是不可能的 – 每次调用.bind都会创建一个新的独立函数,如果传递的函数与传递给addEventListener的函数相同(===),你只能调用removeEventListener来删除一个监听器(就像.includes用于数组,或.has用于集合)：

const fn = () => 'foo';
console.log(fn.bind(window) === fn.bind(window));

作为解决方法,您可以将绑定函数分配给实例的属性：

class MyEl extends HTMLButtonElement {
  constructor() {
    super();
    this.clickCount = 0;
    this.boundListener = this.clickHandler.bind(this);
    window.addEventListener('click', this.boundListener);
  }
  
  clickHandler(e) {
    this.textContent = `clicked ${++this.clickCount} times`;
    window.removeEventListener('click', this.boundListener);
  }
}

customElements.define('my-el', MyEl, { extends: 'button' });

<button is="my-el" type="button">Click me</button>

标签：javascript,ecmascript-6,addeventlistener,custom-element,removeeventlistener
来源： https://codeday.me/bug/20190607/1193634.html