小编Kir*_*tov的帖子

我有代码:

// lib.js
var a = "a";
export var b = "b";

// main.js
console.log(a); // "a" variable is not available in a global scope
import {b} from "lib";
console.log(a); // is "a" variable available in a global scope or only in a module scope?

我可以在模块导入后在全局范围内使用"a"变量,还是仅在模块范围内可用？ES6模块是否具有类似这样的工作原理:

// module    
exports.module1 = (function(){ var a = "a"; })(); // "a" variable is not available in a global scope

#1

你好.我有代码:

class Component extends React.Component
{
  render()
  {
    this.props.nested.prop = this.props.parse.nested.prop;
    return <div>Component</div>;
  }
  componentDidMount()
  {
    console.log(this.props.nested.prop);
  }
}
Component.defaultProps = 
{
  nested:
  {
    prop: "default"
  }
};

const obj1 = 
{
  nested:
  {
    prop: "obj1"
  }
};
const obj2 = 
{
  nested:
  {
    prop: "obj2"
  }
};

class Application extends React.Component
{
  render()
  {
    return (
     <div>
        <Component parse={obj1}/>
        <Component parse={obj2}/>
    </div>
    );
  }
}

React.render(<Application />, document.getElementById('app'));
//console output:
//"obj2"
//"obj2"

为什么我为每个组件获得2个独立组件的1个变量引用而不是2个nested的nested.prop？为什么this.props在安装后只保存组件的所有实例的最后设置值？这是正常的行为吗？我认为正确的行为是针对不同的实例具有不同的属性值.

PS我在这里测试了这段代码.

#2

jimfb …

如何在没有迭代的情况下获取ES6 Map/Set的最后一个元素(forEach或for for)通过容器的整个长度？

我无法正确加载gulp babel/polyfill.在我的情况下,Array.from方法是未定义的.但是,如果尝试browser-polyfill.js使用gulp 加载,.add(require.resolve("babel/polyfill"))我会收到错误"only one instance of babel/polyfill is allowed".源代码是正确的,因为我用babel测试了它browser-polyfill.js.

源代码:

//Lib.js
export default class Lib
{
  constructor()
  {
    var src = [1, 2, 3];
    this.dst = Array.from(src);
  }
  foo()
  {
    return this.dst;
  }
}

//main.js
import Lib from "./Lib";

var l = new Lib();
console.log(l.foo()); //Uncaught TypeError: Array.from is not a function

Gulpfile:

var gulp       = require('gulp');
var sourcemaps = require('gulp-sourcemaps');
var source     = require('vinyl-source-stream');
var buffer     = require('vinyl-buffer'); …

我无法获取自定义画布元素的绘图上下文。

var customCanvas      = Object.create(HTMLCanvasElement.prototype),
    canvasConstructor = document.registerElement("custom-canvas", { prototype: customCanvas }),
    canvas            = document.createElement("custom-canvas"),
    ctx               = canvas.getContext("2d"); // Uncaught TypeError: Illegal invocation

是错误、遗漏还是其他原因？

PS 我正在寻找仅基于 chromium 的浏览器的解决方案。