声明式编程和命令式编程有什么区别

2025-03-15 05:21:39
推荐回答(1个)
回答1:

1、命令式编程:命令“机器”如何去做事情(how),这样不管你想要的是什么(what),它都会按照你的命令实现。

声明式编程:告诉“机器”你想要的是什么(what),让机器想出如何去做(how)。

2、声明式编程和命令式编程的代码例子
举个简单的例子,假设我们想让一个数组里的数值翻倍。
(1)用命令式编程风格实现,像下面这样:
var numbers = [1,2,3,4,5]
var doubled = []
for(var i = 0; i < numbers.length; i++) {
var newNumber = numbers[i] * 2
doubled.push (newNumber)
}
console.log (doubled) //=> [2,4,6,8,10]
我们直接遍历整个数组,取出每个元素,乘以二,然后把翻倍后的值放入新数组,每次都要操作这个双倍数组,直到计算完所有元素。

(2)而使用声明式编程方法,我们可以用 Array.map 函数,像下面这样:
var numbers = [1,2,3,4,5]
var doubled = numbers.map (function (n) {
return n * 2
})
console.log (doubled) //=> [2,4,6,8,10]

map利用当前的数组创建了一个新数组,新数组里的每个元素都是经过了传入map的函数(这里是function (n) { return n*2 })的处理。
map函数所做的事情是将直接遍历整个数组的过程归纳抽离出来,让我们专注于描述我们想要的是什么(what)。注意,我们传入map的是一个纯函数;它不具有任何副作用(不会改变外部状态),它只是接收一个数字,返回乘以二后的值。

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