var array = [1,2,3,4,5,6,7];  for (var i = 0; i < array.length; i) {  console.log(i,array[i]);  }  

    for(let index in array) {  console.log(index,array[index]);  };  

array.forEach(v=>{  console.log(v);
});

array.forEach（function(v){  console.log(v);
});

var A = {a:1,b:2,c:3,d:"hello world"};
for(let k in A) {  console.log(k,A[k]);
} 

    for(let v of array) {  console.log(v);  };  

let s = "helloabc";

for(let c of s) {

console.log(c);

}

    var set = new Set();  set.add("a").add("b").add("d").add("c");  var map = new Map();  map.set("a",1).set("b",2).set(999,3);  for (let v of set) {  console.log(v);  }  console.log("--------------------");  for(let [k,v] of map) {  console.log(k,v);  }  

let array1 = ['a','b','c'];
for (let i = 0;i < array1.length;i++){console.log(array1[i]);  // a  b  c
}

Array.forEach(function(value , index , array){ //value为遍历的当前元素，index为当前索引，array为正在操作的数组//do something
},thisArg)      //thisArg为执行回调时的this值

var array1 = [1,2,3,4,5];var x = array1.forEach(function(value,index){console.log(value);   //可遍历到所有数组元素return value + 10
});
console.log(x);   //undefined    无论怎样，总返回undefinedvar y = array1.map(function(value,index){console.log(value);   //可遍历到所有数组元素return value + 10
});
console.log(y);   //[11, 12, 13, 14, 15]   返回一个新的数组

let divList = document.querySelectorAll('div');   //divList不是数组，而是nodeList//进行转换后再遍历
[].slice.call(divList).forEach(function(element,index){element.classList.add('test')
})Array.prototype.slice.call(divList).forEach(function(element,index){element.classList.remove('test')
})[...divList].forEach(function(element,index){   //<strong>ES6写法</strong>//do something
})

let array2 = ['a','b','c']
let obj1 = {name : 'lei',age : '16'
}for(variable  in array2){   //variable  为 indexconsole.log(variable )   //0 1 2
}for(variable  in obj1){   //variable 为属性名console.log(variable)   //name age
}

let array2 = ['a','b','c']
let obj1 = {name : 'lei',age : '16'
}for(variable  of array2){   //<strong>variable  为 value</strong>console.log(variable )   //'a','b','c'
}for(variable  of obj1){  //<strong>普通对象不能这样用</strong>console.log(variable)   // 报错 ： main.js:11Uncaught TypeError: obj1[Symbol.iterator] is not a function
}<br><br>let divList = document.querySelectorAll('div');<br><br>for(element of divlist){  //可遍历所有的div节点<br>　　//do something <br>}

Object.prototype.objCustom = function () {};
Array.prototype.arrCustom = function () {};let iterable = [3, 5, 7];
iterable.foo = "hello";for (let i in iterable) {console.log(i); // logs 0, 1, 2, "foo", "arrCustom", "objCustom"
}for (let i of iterable) {console.log(i); // logs 3, 5, 7
}