mongodb 数组化简_使用数组化简

亦凉 2023-02-21 14:29 31阅读 0赞

mongodb 数组化简

Every developer who specializes in any programming language will tell you there's a powerful tool the language provides that they rarely use and wish they knew more about. For me, it's `Array.prototype.reduce`. I quite enjoy the other `Array` methods like `map`, `filter`, and `find`, but `reduce` is one that I knew was powerful but never really had much use for.

每个专门研究任何编程语言的开发人员都会告诉您，有一个功能强大的工具，该语言提供了他们很少使用并且希望他们了解更多的工具。 对我来说，它是`Array.prototype.reduce` 。 我非常喜欢其他`Array`方法，例如`map` ， `filter`和`find` ，但是`reduce`是我知道功能强大但从未真正使用过的方法。

It wasn't until I was refactoring some of the [Firefox DevTools Debugger code][] that I found a great use case for `reduce` \-- one I plan on using in the future.

直到我重构了一些[Firefox DevTools Debugger代码后][Firefox DevTools Debugger code] ，我才发现了一个很好的`reduce`使用案例-我计划在将来使用。

Methods like `forEach` and `map` were created to [avoid side effects][], and `reduce` is no exception. In this case, however, `reduce` can return an `Object` other than an `Array`. Take this case for example:

创建了诸如`forEach`和`map`方法来[避免副作用][avoid side effects] ，并且`reduce`也不例外。 在这种情况下，然而， `reduce`可以返回一个`Object`不是其他`Array` 。 以这种情况为例：

// Samples sources
    const sources = [
      {
        id: "server1.conn13.child1/39",
        url: "https://davidwalsh.name/"
      },
      {
        id: "server1.conn13.child1/37",
        url: "https://davidwalsh.name/util.js"
      }
    ];
    
    // Return an object of sources with the keys being "id"
    const sourcesMap = sources.reduce((map, source) => {
      map[source.id] = source
      return map;
    }, {});

In the example above, we take an array of `Source` objects and return a single object literal with each `Source`'s `id` as the key:

在上面的示例中，我们获取一个`Source`对象数组，并返回一个对象常量，其中每个`Source`的`id`作为键：

{
      "server1.conn13.child1/39": {
        "id": "server1.conn13.child1/39",
        "url": "https://davidwalsh.name/"
      },
      "server1.conn13.child1/37": {
        "id": "server1.conn13.child1/37",
        "url": "https://davidwalsh.name/util.js"
      }
    }

Note that the `{}`, which is the last argument to `reduce`, is starting/default object to be returned. If there were no items in the array, `{}` would be returned. Also appreciate that an array method returns an object literal and not a modified array!

注意， `{}`是`reduce`的最后一个参数，是要返回的起始对象/默认对象。 如果数组中没有项目，将返回`{}` 。 还应该意识到，数组方法返回的是对象常量而不是修改后的数组！

It's crazy that I've not used `reduce` more, but that's just life in our industry -- we all have a few APIs we just haven't used much of. What feature of JavaScript have you frequently seen but not used?

疯狂的是我没有使用过`reduce`更多的东西，但这只是我们行业中的生活-我们都有一些API，我们只是很少使用。 您经常看到但不使用JavaScript的哪些功能？

> 翻译自: [https://davidwalsh.name/using-array-reduce][https_davidwalsh.name_using-array-reduce]

mongodb 数组化简

[Firefox DevTools Debugger code]: https://github.com/devtools-html/debugger.html
[avoid side effects]: https://davidwalsh.name/preventing-sideeffects-javascript
[https_davidwalsh.name_using-array-reduce]: https://davidwalsh.name/using-array-reduce