如何在es6 / javascript中阅读功能组合？

问题描述：

背景

组合将两个函数合在一起，形成第三个函数，功能是另一个的输入。

Composition is putting two functions together to form a third function where the output of one function is the input of the other.

无论我看多少，我都在努力阅读它。特别是为什么 compose（） return => （a）=> 捕获本地范围内的 121.2121212 。另外我也努力争取最终的fn f（g（a））将会看到所有的值/ fn存在使用变量。

No matter how much I look at this I struggle with how to read it. In particular why the compose() return => (a) => captures the 121.2121212 in local scope. Also I struggle with how final fn f(g(a)) would look with all the values/fn present w/o the use of variables.

问题：有没有人有任何技术或图表来快速阅读这样的示例;我如何进行智能调试并按照功能流程？

Question: Does anyone have any techniques or diagrams for quickly reading examples like this; how can I mentally debug and follow the function flow?

参考：

const compose = (f, g) => (a) => f(g(a)) // Definition
const floorAndToString = compose((val) => val.toString(), Math.floor) // Usage

floorAndToString(121.212121) // '121'

答

如TJ所述Crowder，它经常帮助重写箭头功能作为常规功能。所以函数：

As mentioned by T.J. Crowder, it often helps rewriting arrow functions as regular functions. So the function:

const compose = (f, g) => (a) => f(g(a))

可以重写为：

function compose (f, g) {
    return function (a) {
        return f(g(a));
    }
}

现在可能更明显的是发生了什么。所以现在让我们重写其他部分：

Now it is perhaps more obvious what's going on. So now let's rewrite the other parts:

const floorAndToString = compose((val) => val.toString(), Math.floor)

可以重写为：

function convertToString (val) { return val.toString() };

const floorAndToString = compose(convertToString, Math.floor);

现在可能更明显的是，撰写函数将返回函数：

Now it may be more obvious that the compose function will return the function:

// remember that we pass `convertToString` as `f`
// and `Math.floor` as `g`:

function (a) {
    return convertToString(Math.floor(a));
}

所以很明显，函数 floorAndToString 只返回 convertToString（Math.floor（a））的结果。没有什么特别的 compose ，它捕获 121.2121212 ，因为它没有。而是创建一个函数，其中 121.2121212 可以作为参数传递给 convertToString（Math.floor（a））。

So it's obvious that the function floorAndToString simply returns the result of convertToString(Math.floor(a)). There is nothing special about compose that captures 121.2121212 because it doesn't. Instead it creates a function where 121.2121212 can be passed as an argument to convertToString(Math.floor(a)).

如何在es6 / javascript中阅读功能组合？

相关推荐