Although a for loop will work for these tasks, we can take advantage of a method like ... of functions in JavaScript. We'll write the code four times, making it increasingly efficient and expressive ...

map 方法是 JavaScript 数组原型 的众多方法之一 ... Every once in a while you'll come across a situation where it comes in handy—for example, when chaining array methods or when you don't have the array bound to a ...