for in
语句可以遍历对象中所有的属性。枚举包括函数和原型属性。
var fruit = {
apple: 2,
orange:5,
pear:1
},
sentence = 'I have ',
quantity;
for (kind in fruit){
quantity = fruit[kind];
sentence += quantity+' '+kind+
(quantity===1?'':'s')+
', ';
}
// The following line removes the trailing coma.
sentence = sentence.substr(0,sentence.length-2)+'.';
// I have 2 apples, 5 oranges, 1 pear.