for in
枚举对象、数组
var obj = {
a: 1,
b: [],
c: function () {}
};
for (var key in obj) {
console.log(key);
}
var arr = [3, 5, 7];
for (var i in arr) {
console.log(i);
}
//--------------
var arr = [3, 5, 7];
for (var i in arr) {
console.log(i, arr[i]);
}
//--
Object.prototype.objCustom = function() {};
Array.prototype.arrCustom = function() {};
var arr = ...
