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用 JavaScript 中的蹦床函数实现安全递归 #7063

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用JavaScript中的蹦床函数实现安全递归
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更新使用JavaScript中的蹦床函数实现安全递归
Gesj-yean May 19, 2020
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38 changes: 19 additions & 19 deletions article/2020/safe-recursion-with-trampoline-in-javascript.md
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Expand Up @@ -2,16 +2,16 @@
> * 原文作者：[Valeriy Baranov](https://medium.com/@baranovxyz)
> * 译文出自：[掘金翻译计划](https://github.com/xitu/gold-miner)
> * 本文永久链接：[https://github.com/xitu/gold-miner/blob/master/article/2020/safe-recursion-with-trampoline-in-javascript.md](https://github.com/xitu/gold-miner/blob/master/article/2020/safe-recursion-with-trampoline-in-javascript.md)
> * 译者：
> * 校对者：
> * 译者：[Gesj-yean](https://github.com/Gesj-yean)
> * 校对者：[cyz980908](https://github.com/cyz980908)，[z0gSh1u](https://github.com/z0gSh1u)

# Safe Recursion with Trampoline in JavaScript
# 使用JavaScript中的蹦床函数实现安全递归

![Photo by [Charles Cheng](https://unsplash.com/@charlesc7?utm_source=medium&utm_medium=referral) on [Unsplash](https://unsplash.com?utm_source=medium&utm_medium=referral)](https://cdn-images-1.medium.com/max/7274/0*9Sxt2ppwVpNELxC0)
![来自[Charles Cheng](https://unsplash.com/@charlesc7?utm_source=medium&utm_medium=referral) 在 [Unsplash](https://unsplash.com?utm_source=medium&utm_medium=referral)](https://cdn-images-1.medium.com/max/7274/0*9Sxt2ppwVpNELxC0)

Using recursion in JavaScript is not safe — consider trampoline. This converts recursion to a `while` loop to get around JavaScript’s limitations and prevent an overflow.
在 JavaScript 中使用递归是不安全的，请考虑使用蹦床函数。它将递归转化为 `while` 循环去绕过 JavaScript 的限制，目的是为了防止溢出。

An idiomatic example of a recursive function is a factorial calculation. We call `factorial` function `n` times to get a result. Every call will add one more `factorial` function to the call stack.
一个典型的递归函数就是阶乘计算。我们调用 `factorial` 函数 `n` 次来得到一个结果。每次调用都会向调用的堆栈添加一个 `factorial` 函数。

```JavaScript
function factorial(n) {
Expand All @@ -22,7 +22,7 @@ function factorial(n) {
console.log(factorial(5)); // 120
```

Recursion in JavaScript is mostly a sign of code smell and generally should be avoided. The reason is that JavaScript is a stack-based language, there is no tail call optimization yet. If you execute the following snippet, you will get a RangeError: Maximum call stack size exceeded.
JavaScript 中的递归通常是代码出现问题的象征，通常应该避免使用。因为 JavaScript 是一种基于堆栈的语言，但目前没有尾调用优化。如果你运行了以下代码，将会报错 RangeError: Maximum call stack size exceeded，意思是超过最大调用堆栈大小。

```JavaScript
function recursiveFn(n) {
Expand All @@ -33,7 +33,7 @@ function recursiveFn(n) {
recursiveFn(100000); // RangeError: Maximum call stack size exceeded
```

Still, there are situations when you want to use a recursive function. A realistic one would be to traverse a `DOM` tree or any other tree-like structure.
不过，也有需要使用递归函数的情况。例如，遍历 `DOM` 树或其他的树形结构。

```JavaScript
function traverseDOM(tree) {
Expand All @@ -42,9 +42,9 @@ function traverseDOM(tree) {
}
```

#### Trampoline — a safe way to use recursion in JavaScript.
#### 蹦床函数 —— JavaScript中的安全递归方式
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With `trampoline`, your transform recursive function into a `while` loop:
使用 `蹦床函数`，你可以将递归函数转化为 `while` 循环：

```JavaScript
function trampoline(f) {
Expand All @@ -58,12 +58,12 @@ function trampoline(f) {
}
```

Let's rewrite the `factorial` function to use `trampoline`. We need to:
让我们用 `蹦床函数` 去重写一个 `阶乘` 函数。我们需要去：

1. return a value in a base case.
2. return a function to be called in other cases.
1. 在基本情况下返回一个值。
2. 在其他情况下返回要调用的函数。

We also add accumulator argument for our internal implementation of `_factorial`.
我们还为 `_factorial` 的内部实现添加了累加器参数。

```JavaScript
const factorial = trampoline(function _factorial(n, acc = 1) {
Expand All @@ -74,7 +74,7 @@ const factorial = trampoline(function _factorial(n, acc = 1) {
console.log(factorial(5));
```

Our `recursiveFn` can be rewritten similar to `factorial`, but we do not need an accumulator to track state. This implementation can be safely run even for millions of iterations.
`recursiveFn` 可以像 `factorial`一样被重写，但我们不需要累加器去跟踪状态。这个实现方式甚至可以安全的运行数百万次的迭代。

```JavaScript
const recursiveFn = trampoline(function _recursiveFn(n) {
Expand All @@ -86,15 +86,15 @@ recursiveFn(100000);
console.log('No range error!');
```

Next time you want to use recursion, try `trampoline`!
下一次你想使用递归的时候，试试 `蹦床函数` 吧！

You can try `trampoline` in this [CodePen](https://codepen.io/baranovxyz/pen/zYvjKGN).
你可以尝试 `蹦床函数` 在这里 [CodePen](https://codepen.io/baranovxyz/pen/zYvjKGN)。

---

Trampoline is not a popular technique. Even in ramda and lodash, there are no trampoline helpers.
蹦床函数并不是一种流行的技术。即使在 ramda 和 lodash 中，也没有提供蹦床函数。

Thanks to Kyle Simpson for the inspiration about trampolines.
感谢 Kyle Simpson 为我提供了蹦床函数的灵感。

> 如果发现译文存在错误或其他需要改进的地方，欢迎到 [掘金翻译计划](https://github.com/xitu/gold-miner) 对译文进行修改并 PR，也可获得相应奖励积分。文章开头的 **本文永久链接** 即为本文在 GitHub 上的 MarkDown 链接。

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