javascript - 扩展 HTMLElement : Constructor fails when webpack was used

Question

我将以下 TypeScript 程序转换为 ES5:

文件 1:

class BaseElement extends HTMLElement {
    constructor() {
        super();
    }
}

文件 2:

import {BaseElement} from './BaseElement';

class MyElement extends BaseElement {
    constructor() {
        super();
    }
}

var el = new MyElement();

将所有内容手动放入文件中，代码运行良好并在浏览器中执行，HTMLElement 的构建没有问题。但是，一旦我通过 webpack 打包它，我就会收到以下错误消息:

Uncaught TypeError: Failed to construct 'HTMLElement': Please use the 'new' operator, this DOM object constructor cannot be called as a function.

不使用webpack，构建如下JS代码:

var __extends = (this && this.__extends) || function (d, b) {
    for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
    function __() { this.constructor = d; }
    d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};
var BaseElement = (function (_super) {
    __extends(BaseElement, _super);
    function BaseElement() {
        _super.call(this);
    }
    return BaseElement;
}(HTMLElement));
var MyElement = (function (_super) {
    __extends(MyElement, _super);
    function MyElement() {
        _super.call(this);
    }
    MyElement.prototype.createdCallback = function () {
        this.innerHTML = "lol";
    };
    return MyElement;
}(BaseElement));
var el = new MyElement();

使用webpack，构造如下代码:

var __extends = (this && this.__extends) || function (d, b) {
    for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
    function __() { this.constructor = d; }
    d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};
/******/ (function(modules) { // webpackBootstrap
/******/    // The module cache
/******/    var installedModules = {};

/******/    // The require function
/******/    function __webpack_require__(moduleId) {

/******/        // Check if module is in cache
/******/        if(installedModules[moduleId])
/******/            return installedModules[moduleId].exports;

/******/        // Create a new module (and put it into the cache)
/******/        var module = installedModules[moduleId] = {
/******/            exports: {},
/******/            id: moduleId,
/******/            loaded: false
/******/        };

/******/        // Execute the module function
/******/        modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);

/******/        // Flag the module as loaded
/******/        module.loaded = true;

/******/        // Return the exports of the module
/******/        return module.exports;
/******/    }


/******/    // expose the modules object (__webpack_modules__)
/******/    __webpack_require__.m = modules;

/******/    // expose the module cache
/******/    __webpack_require__.c = installedModules;

/******/    // __webpack_public_path__
/******/    __webpack_require__.p = "";

/******/    // Load entry module and return exports
/******/    return __webpack_require__(0);
/******/ })
/************************************************************************/
/******/ ([
/* 0 */
/***/ function(module, exports, __webpack_require__) {

    __webpack_require__(1);
    __webpack_require__(2);

/***/ },
/* 1 */
/***/ function(module, exports) {

    "use strict";
    var BaseElement = (function (_super) {
        __extends(BaseElement, _super);
        function BaseElement() {
            _super.call(this);
        }
        return BaseElement;
    }(HTMLElement));
    exports.BaseElement = BaseElement;


/***/ },
/* 2 */
/***/ function(module, exports, __webpack_require__) {

    "use strict";
    var BaseElement_1 = __webpack_require__(1);
    var MyElement = (function (_super) {
        __extends(MyElement, _super);
        function MyElement() {
            _super.call(this);
        }
        MyElement.prototype.createdCallback = function () {
            this.innerHTML = "lol";
        };
        return MyElement;
    }(BaseElement_1.BaseElement));
    exports.MyElement = MyElement;
    // TODO: inject
    var p = new MyElement();
/***/ }
/******/ ]);

基本上，webpack 将任何模块放入一个函数中，并在它们之间维护一个导出变量，但是 HTMLElement 的构造失败了。没有 webpack(上面的代码)，它工作正常。

有什么想法吗？

Answer 1

这是转译问题。如果您正在转译或使用 ES5，那么您需要为支持 native Web 组件的浏览器捆绑 native-shim。( https://github.com/webcomponents/custom-elements/blob/master/src/native-shim.js )

ES5-style classes don't work with native Custom Elements because the HTMLElement constructor uses the value of new.target to look up the custom element definition for the currently called constructor. new.target is only set when new is called and is only propagated via super() calls. super() is not emulatable in ES5. The pattern of SuperClass.call(this)`` only works when extending other ES5-style classes, and does not propagatenew.target`.

查看问题讨论https://github.com/webcomponents/custom-elements/issues/29