In ES6, IIFE is not necessary: // IIFE写法 (function () { var tmp = ...; ... }()); // 块级作用域写法 { let tmp = ...; ... } 另外,ES6也规定,函数本身的作用域,在其所在的块级作用域之内. function f() { console.log('I am outside!'); } (function () { if(false) { // 重复声明一次函数f function f() {…

The basic syntax of an anoymous function used as a block scope (often called a private scope) is as follows: (function(){ // block code here }) (); A variable is just a representation of another value, so the variable can be replaced with the actual…

Fiald case 1: let can work in it's block { let a = 10; var b = 1; } a // ReferenceError: a is not defined. b Case 2: Let has no "Hosting" Problem function do_something() { console.log(foo); // ReferenceError let foo = 2; } function do_something(…

var message = "Hi"; { var message = "Bye"; } console.log(message); //Bye The message inside the block still has impact on the outside. Just remember that something like for, while if ... block, they don't create new scope. function blo…

Introduction 本系列文章为You Don't Know JS的读书笔记. 书籍地址:https://github.com/getify/You-Dont-Know-JS Scope From Functions 一个非常普遍的观点是,Javascript的作用域是基于函数的,这个观点其实并不是那么正确,不过,让我们来先看一下函数级别的作用域. function foo(a) { var b = 2; // some code function bar() { // ... } //…

View on GitHub Note: A commonly accepted practice is to use const except in cases of loops and reassignment. However, in this resource I'll be using let in place of var for all ES6 examples. Variable: x Object: obj Array: arr Function: func Parameter…

'const' keyword is for creating a read only variable, something you can never change once created. 'const' likes 'let' keyword alos has block scope. describe("using const", function(){ it("will make a variable read-only", function(){ c…

Content What is Scope? Lexical Scope Function Vs. Block Scope Hoisting Scope Closures Appendix: Dynamic Scope Polyfilling Block Scope Lexical-this Thank You's Chapter1: What is Scope? In fact, the ability to store values and pull values out of variab…

越来越多的开源库开始使用ES2015来构建代码了,大家知道ES6=ES2015,ES6在2015年被ECMAScript标准化组织approve,各大浏览器厂商要完全支持ES6的强大功能还须一些时日,对于喜爱新尝试的同学难道只有干等吗?幸运的是有了babel,traceur等transpiler的帮助,我们根本不用等待浏览器原生支持ES6才开始使用新技术了!其实babel做的事情很简单,他就是把es6的代码转换成浏览器认识的ES5代码.简单举一个例子,比如ES6中引入的语言原生支持模块的关键字i…

介绍 ES6:ECMScript6 首先,一个常见的问题是,ECMAScript 和 JavaScript 到底是什么关系? ECMAScript是一个国际通过的标准化脚本语言: JavaScript由ECMAScript和DOM.BOM三者组成: 可以简单理解为:ECMAScript是JavaScript的语言规范,JavaScript是ECMAScript的实现和扩展: 2011 年,ECMAScript 5.1 版发布.之前我们大部分人用的也就是ES5. 2015 年 6 月,ECMASc…