JavaScript 中 forEach、for in 与 for of 遍历用法详解

var array = [1,2,3,4,5,6];
/**
* currentValue 当前元素
* index 当前元素的索引值
* arr 当前元素所属的数组对象
**/
array.forEach(function(currentValue, index, arr) {
    console.log("index: " + index + "; currentValue: ", currentValue);
});

var object = {"a":1, "b":2, "c":3};
/**
* currentValue 当前元素
* index 当前元素的索引值
* arr 当前元素所属的数组对象
**/
Object.keys(object).forEach(function(currentValue, index, arr) {
    console.log("index: " + index + "; currentValue: ", currentValue);
});

var array = [1,2,3,4,5,6];
for (var index in array) {
    console.log("index: " + index + "; currentValue: ", array[index]);
}

var object = {"a":1, "b":2, "c":3};
for (var index in object) {
    console.log("index: " + index + "; currentValue: ", object[index]);
}

var array = [1,2,3,4,5,6];
for (var varlue of array) {
    console.log("currentValue: ", varlue);
}

var obj = {
    a:1,
    b:2,
    c:3
};
obj[Symbol.iterator] = function(){
    var keys = Object.keys(this);
    var count = 0;
    return {
        next(){
            if(count < keys.length) {
                return {value:obj[keys[count++]], done:false};
            }else{
                return {value:undefined, done:true};
            }
        }
    }
};
for(var k of obj){
    console.log(k);
}

var obj = {
    a:1,
    b:2,
    c:3
};
obj[Symbol.iterator] = function*(){
    var keys = Object.keys(obj);
    for(var k in keys){
        yield [k, keys[k]]
    }
};
for(var [k, v] of obj){
    console.log(k, v);
}