详解JS中遍历语法的比较

let arr = [1,2,3,4,5];

for (var index = 0; index < arr.length; index++) {
 console.log(myArray[index]); // 1 2 3 4 5
} 

let arr = [1,2,3,4,5];

arr.forEach((element,index) => {
  console.log(element); // 1 2 3 4 5
});

let obj = {
  name: 'cloud',
  phone: '157xxxx2065'
}
 
for (let prop in obj) {
  console.log(prop); // name phone
}

let arr = [10, 20, 30, 40, 50];
 
for (let prop in arr) {
  console.log(prop); // '0' '1' '2' '3' '4'
}

for (var n of fibonacci) {
 if (n > 1000)
  break;
 console.log(n);
}

 // demo
let arr = ['a', 'b', 'c'];
for (let pair of arr.entries()) {
 console.log(pair);
}
// [0, 'a']
// [1, 'b']
// [2, 'c']

// 字符串
let str = "hello";

for (let s of str) {
 console.log(s); // h e l l o
}

// DOM NodeList对象
let paras = document.querySelectorAll("p");

for (let p of paras) {
 p.classList.add("test");
}

// arguments对象
function printArgs() {
 for (let x of arguments) {
  console.log(x);
 }
}
printArgs('a', 'b');
// 'a'
// 'b'

let arrayLike = { length: 2, 0: 'a', 1: 'b' };

// 报错
for (let x of arrayLike) {
 console.log(x);
}

// 正确
for (let x of Array.from(arrayLike)) {
 console.log(x); // 'a' // 'b'
}

let es6 = {
 edition: 6,
 committee: "TC39",
 standard: "ECMA-262"
};

for (let e in es6) {
 console.log(e);
}
// edition
// committee
// standard

for (let e of es6) {
 console.log(e);
}
// TypeError: es6 is not iterable

for (var key of Object.keys(someObject)) {
 console.log(key + ': ' + someObject[key]);
}