var obj = { '1' : 'apple', '2' : 'orange', '3' : 'pear' };

var arrMsg = ['apple', 'orange', 'pear'];

var array  = [{'111': 'apple'}, {'222': 'orange'}];

for(var key in obj){    
    console.log(key);      //輸出為 1  2  3 
    console.log(obj[key]); //輸出為 apple orange pear
}

$.each(obj, function(i) {
    alert(i);   	//輸出為 1 2 3 
    alert(obj[i]);	//輸出為 apple orange pear
});

for(var [key,value] in obj){    
    console.log(key);      //輸出為 1 2 3
    console.log(value);    //輸出為 undefined undefined undefined
}


// 以下有錯，待驗證
for(var (key,value) in obj){    
    console.log(key);      //輸出為 1 2 3
    console.log(value);    //輸出為 apple orange pear
}
 

for(var val in arrMsg){     
    console.log(val);        //輸出為  0 1 2
}

for(var val in arrMsg){     
    console.log(arrMsg[val]);      //輸出為  apple orange pear
}

for(var val in arrMsg){     
    console.log(val);      //輸出為  apple orange pear
}

原文有錯，略改

https://blog.csdn.net/u013746071/article/details/80004475