# 1.2.5.6.危險小叮嚀：陣列與 for in

* 陣列是物件, 而成員是被新增的屬性

```
var arr = ['John', 'Jane', 'Jim']


for (var prop in arr) {
    console.log(prop + ':' + arr[prop])
}


Array.prototype.myCustomFeature = 'cool!'
```