JavaScript ES6 import/export 和 class 扩展

Question

我构建了一个自定义元素，它是一个汉堡包按钮，现在我正在使用侧边导航。在这侧导航中，我想使用我的汉堡包按钮，所以我尝试导出与我的按钮相对应的 HCHamburger class，并将其导入我的 SideNav class。这个想法是在侧边导航打开时为我的按钮位置设置动画。我尝试用 HCHamburger 扩展我的 SideNav class 但我收到以下错误：Uncaught TypeError: Failed to construct 'HTMLElement': Please use the 'new' operator, this DOM object constructor cannot be called as a function.

我的 HCHambuger class 看起来像这样：

'use strict';

export default class HCHamburger extends HTMLElement {

    get menuButton() {
        if (!this._menuButton) {
            this._menuButton = this.querySelector('.hamburger-menu');
        }

        return this._menuButton;
    }

    get bar() {
        if (!this._bar) {
            this._bar = this.querySelector('.bar');
        }

        return this._bar;
    }

    attachedCallback() {
        this.menuButton.addEventListener('click', _ => {
            const sideNavContainerEl = document.querySelector('.js-side-nav-container');
            this.bar.classList.toggle("animate");
            if (sideNavContainerEl.getAttribute('nav-opened') == 'false') {
                this.openMenuButton(sideNavContainerEl);
            } else {
                this.closeMenuButton(sideNavContainerEl);
            }
        });
    }

    sayHello() {
        console.log('TOTO');
    }

    openMenuButton(sideNavContainerEl) {
        this.style.transform = `translateX(${sideNavContainerEl.offsetWidth}px)`;
    }

    closeMenuButton(sideNavContainerEl) {
        this.style.transform = `translateX(0px)`;
    }
}

document.registerElement('hc-hamburger', HCHamburger);

我的 SideNav class 是这样的：

'use strict';

import Detabinator from './detabinator.js';
import HCHamburger from './hamburger.js';

class SideNav extends HCHamburger {
  constructor () {
    super();
    this.toggleMenuEl = document.querySelector('.js-menu');
    this.showButtonEl = document.querySelector('.js-menu-show');
    this.hideButtonEl = document.querySelector('.js-menu-hide');
    this.sideNavEl = document.querySelector('.js-side-nav');
    this.sideNavContainerEl = document.querySelector('.js-side-nav-container');
    // Control whether the container's children can be focused
    // Set initial state to inert since the drawer is offscreen
    this.detabinator = new Detabinator(this.sideNavContainerEl);
    this.detabinator.inert = true;

    this.toggleSideNav = this.toggleSideNav.bind(this);
    this.showSideNav = this.showSideNav.bind(this);
    this.hideSideNav = this.hideSideNav.bind(this);
    this.blockClicks = this.blockClicks.bind(this);
    this.onTouchStart = this.onTouchStart.bind(this);
    this.onTouchMove = this.onTouchMove.bind(this);
    this.onTouchEnd = this.onTouchEnd.bind(this);
    this.onTransitionEnd = this.onTransitionEnd.bind(this);
    this.update = this.update.bind(this);

    this.startX = 0;
    this.currentX = 0;
    this.touchingSideNav = false;

    this.supportsPassive = undefined;
    this.addEventListeners();
  }

  // apply passive event listening if it's supported
  applyPassive () {
    if (this.supportsPassive !== undefined) {
      return this.supportsPassive ? {passive: true} : false;
    }
    // feature detect
    let isSupported = false;
    try {
      document.addEventListener('test', null, {get passive () {
        isSupported = true;
      }});
    } catch (e) { }
    this.supportsPassive = isSupported;
    return this.applyPassive();
  }

  addEventListeners () {
    this.toggleMenuEl.addEventListener('click', this.toggleSideNav);
    this.sideNavEl.addEventListener('click', this.hideSideNav);
    this.sideNavContainerEl.addEventListener('click', this.blockClicks);

    this.sideNavEl.addEventListener('touchstart', this.onTouchStart, this.applyPassive());
    this.sideNavEl.addEventListener('touchmove', this.onTouchMove, this.applyPassive());
    this.sideNavEl.addEventListener('touchend', this.onTouchEnd);
  }

  onTouchStart (evt) {
    if (!this.sideNavEl.classList.contains('side-nav--visible'))
      return;

    this.startX = evt.touches[0].pageX;
    this.currentX = this.startX;

    this.touchingSideNav = true;
    requestAnimationFrame(this.update);
  }

  onTouchMove (evt) {
    if (!this.touchingSideNav)
      return;

    this.currentX = evt.touches[0].pageX;
    const translateX = Math.min(0, this.currentX - this.startX);

    if (translateX < 0) {
      evt.preventDefault();
    }
  }

  onTouchEnd (evt) {
    if (!this.touchingSideNav)
      return;

    this.touchingSideNav = false;

    const translateX = Math.min(0, this.currentX - this.startX);
    this.sideNavContainerEl.style.transform = '';

    if (translateX < 0) {
      this.hideSideNav();
    }
  }

  update () {
    if (!this.touchingSideNav)
      return;

    requestAnimationFrame(this.update);

    const translateX = Math.min(0, this.currentX - this.startX);
    this.sideNavContainerEl.style.transform = `translateX(${translateX}px)`;
  }

  blockClicks (evt) {
    evt.stopPropagation();
  }

  onTransitionEnd (evt) {
    this.sideNavEl.classList.remove('side-nav--animatable');
    this.sideNavEl.removeEventListener('transitionend', this.onTransitionEnd);
  }

  showSideNav () {
    this.sideNavEl.classList.add('side-nav--animatable');
    this.sideNavEl.classList.add('side-nav--visible');
    this.detabinator.inert = false;
    this.sideNavEl.addEventListener('transitionend', this.onTransitionEnd);
  }

  hideSideNav () {
    this.sideNavEl.classList.add('side-nav--animatable');
    this.sideNavEl.classList.remove('side-nav--visible');
    this.detabinator.inert = true;
    this.sideNavEl.addEventListener('transitionend', this.onTransitionEnd);
  }

  toggleSideNav () {
    if (this.sideNavContainerEl.getAttribute('nav-opened') == 'true') {
      this.hideSideNav();
      this.sideNavContainerEl.setAttribute('nav-opened', 'false');
    } else {
      this.showSideNav();
      this.sideNavContainerEl.setAttribute('nav-opened', 'true');
    }
  }
}

new SideNav();

我正在使用 webpack 构建我的 JS 代码，也许这就是我出现问题的原因...我尝试了与 import/export 不同的方法，但没有任何效果。

我想只导出我需要的方法，但它也不起作用。

谢谢

Answer 1

从根本上说，DOM 的 API 和 JavaScript 的继承（目前）只是不匹配。您不能在当前的浏览器上执行 extends HTMLElement 操作。当 custom elements specification settles down and is widely-implemented in its final form, but not right now.

时，您也许可以在某个时候

如果你转译，你会得到你的问题中的错误，因为转译的代码试图按照这些行做一些事情：

function MyElement() {
  HTMLElement.call(this);
}
var e = new MyElement();

如果您不转译（需要浏览器支持 ES2015+），您可能会遇到不同的错误：

TypeError: Illegal constructor

class MyElement extends HTMLElement {
}
let e = new MyElement();

您有几个不涉及从 HTMLElement 继承的选项：包装和原型扩充

环绕

您有一个包装元素的函数。它可能会为单个元素或元素集创建包装器，例如 jQuery；这是一个非常简单的集合示例：

// Constructor function creating the wrapper; this one is set-based
// like jQuery, but unlike jQuery requires that you call it via `new`
// (just to keep the example simple).
function Nifty(selectorOrElementOrArray) {
  if (!selectorOrElementOrArray) {
    this.elements = [];
  } else {
    if (typeof selectorOrElementOrArray === "string") {
      this.elements = Array.prototype.slice.call(
        document.querySelectorAll(selectorOrElementOrArray)
      );
    } else if (Array.isArray(selectorOrElementOrArray)) {
      this.elements = selectorOrElementOrArray.slice();
    } else {
      this.elements = [selectorOrElementOrArray];
    }
  }
}
Nifty.prototype.addClass = function addClass(cls) {
  this.elements.forEach(function(element) {
    element.classList.add(cls);
  });
};

// Usage
new Nifty(".foo").addClass("test");
new Nifty(".bar").addClass("test2");

.test {
  color: green;
}
.test2 {
  background-color: yellow;
}

<div id="test">
  <span class="bar">bar1</span>
  <span class="foo">foo1</span>
  <span class="bar">bar2</span>
  <span class="foo">foo2</span>
  <span class="bar">bar3</span>
</div>

原型增强

您可以增加 HTMLElement.prototype。有赞成也有反对的声音，"against" 主要指出如果多个脚本试图向它添加相同的属性（或者如果 W3C 或 WHAT-WG 添加新的 properties/methods ），这显然是一个非常现实的可能性。但是如果你让你的属性名字不太可能被其他人使用，你可以将这种可能性降到最低：

// Add xyzSelect and xyzAddClass to the HTMLElement prototype
Object.defineProperties(HTMLElement.prototype, {
  "xyzSelect": {
    value: function xyzSelect(selector) {
      return Array.prototype.slice.call(this.querySelectorAll(selector));
    }
  },
  "xyzAddClass": {
    value: function xyzAddClass(cls) {
      return this.classList.add(cls);
    }
  }
});

// Usage
var test = document.getElementById("test");
test.xyzSelect(".foo").forEach(function(e) { e.xyzAddClass("test"); });
test.xyzSelect(".bar").forEach(function(e) { e.xyzAddClass("test2"); });

.test {
  color: green;
}
.test2 {
  background-color: yellow;
}

<div id="test">
  <span class="bar">bar1</span>
  <span class="foo">foo1</span>
  <span class="bar">bar2</span>
  <span class="foo">foo2</span>
  <span class="bar">bar3</span>
</div>

原型增强适用于现代浏览器，也适用于 IE8。它在 IE7 和更早版本中不起作用。

JavaScript ES6 import/export 和 class 扩展

JavaScript ES6 import/export and class extends

html

javascript

ecmascript-6

webpack

es6-class

环绕

原型增强