var arr = ['red', 'green', 'blue']for(let item in arr) {console.log('for in item', item)}/*for in item 0for in item 1for in item 2*/for(let item of arr) {console.log('for of item', item)}/*for of item redfor of item greenfor of item blue*/

 var obj = {'name': 'Jim Green','age': 12}for(let key of obj) {console.log('for of obj', key)}// Uncaught TypeError: obj is not iterable

 for(let key in obj) {console.log('for in key', key)}/*for in key namefor in key age*/

 for(let key of Object.keys(obj)) {console.log('key', key)}/*key namekey age*/

  let arr = [1, 2, 3]arr.set = 'world'  // 手动添加的键Array.prototype.name = 'hello'  // 原型链上的键for(let item in arr) {console.log('item', item)}/*item 0item 1item 2item setitem name*/for(let value of arr) {console.log('value', value)}/*value 1value 2value 3*/

  let arr = [1, 2, 3, 5, 9]arr.forEach(item => {if(item % 2 === 0) {return}console.log('item', item)})/*item 1item 3item 5item 9*/

 for(let item of arr) {if(item % 2 === 0) {break}console.log('item', item)}// item 1

{let a = Symbol('a')let b = Symbol('b')let obj = {[a]: 'hello',[b]: 'world',c: 'es6',d: 'dom'}for(let key in obj) {console.info(key + ' --> ' + obj[key])}/*c --> es6d --> dom*/let objSymbols = Object.getOwnPropertySymbols(obj)console.info(objSymbols)    //  [Symbol(a), Symbol(b)]objSymbols.forEach(item => {console.info(item.toString() + ' --> ' + obj[item])})/*Symbol(a) --> helloSymbol(b) --> world*/// Reflect.ownKeys 方法可以返回所有类型的键名，包括常规键名和Symbol键名let keyArray = Reflect.ownKeys(obj)console.log(keyArray)      //  ["c", "d", Symbol(a), Symbol(b)]
}