Iterate over objects with for ... of

//方法一：
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); 
}

// 方法二
var obj = {
    a:1,
    b:2,
    c:3
};
obj[Symbol.iterator] = function*(){
    var keys = Object.keys(obj);
    for(var k in keys){
        yield [k,obj[k]]
    }
};
 
for(var [k,v] of obj){
    console.log(k,v);
}