.map一个数组，以便它只保留每个元素的前5个字符？

Question

我尝试使用.map函数更改此数组，以便我只有前5个字符，例如＆＃34; 01：00＆＃34;，＆＃34; 02：00＆＃34; ？

这是数组：

["01:00:00 AM", "02:00:00 AM", "03:00:00 AM", "04:00:00 AM", "05:00:00 AM", "06:00:00 AM", "07:00:00 AM", "08:00:00 AM", "09:00:00 AM", "10:00:00 AM", "11:00:00 AM", "12:00:00 PM", "13:00:00 PM", "14:00:00 PM", "15:00:00 PM", "16:00:00 PM", "17:00:00 PM", "18:00:00 PM", "19:00:00 PM", "20:00:00 PM", "21:00:00 PM", "22:00:00 PM", "23:00:00 PM", "00:00:00 AM"]

Answer 1

首先定义一个函数来获取字符串的前5个字符：

function first5(str){return str.substring(0, 5)}

然后将函数传递给array.map：

arr = ["01:00:00 AM", "02:00:00 AM", "03:00:00 AM"]  // you can use your full array here
arr.map(first5) //=> ["01:00", "02:00", "03:00"]

如果你看一下documentation的array.map，它（就像javascript中的许多其他函数一样）将一个函数作为输入。