Typescript --allowJs 如何工作？
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How does Typescript --allowJs work?
提问by Oskar
I have read:
我读过了：
- TypeScript Roadmap 1.8
- JavaScript in TypeScript compilations
- Compilation of Js Files
- Announcing TypeScript 1.8 Beta
but I still don't get how it works and what it is good for. Could someone please explain what it is and when I would want to use it?
但我仍然不明白它是如何工作的以及它有什么好处。有人可以解释一下它是什么以及我什么时候想使用它吗？
采纳答案by Oskar
From Clay Allsopp on Medium:
allowJs is the option newly available in 1.8. The TypeScript compiler will run a quick sanity check on .js files for syntax errors but otherwise passes them straight through to the output directory.
allowJs 是 1.8 中新提供的选项。TypeScript 编译器将对 .js 文件运行快速健全性检查以查找语法错误，否则会将它们直接传递到输出目录。
This is useful when migrating a JavaScript project to TypeScript, that way you don't have to migrate everything at once but instead start writing new code in TypeScript and/or migrate each file one by one. You can find more information about migration from JavaScript to Typescript on the official site for TypeScript that has a tutorial called "Migrating from JavaScript".
这在将 JavaScript 项目迁移到 TypeScript 时非常有用，这样您就不必一次迁移所有内容，而是开始在 TypeScript 中编写新代码和/或逐个迁移每个文件。您可以在 TypeScript 的官方网站上找到有关从 JavaScript 迁移到 Typescript 的更多信息，该站点有一个名为“从 JavaScript 迁移”的教程。
回答by Martin
There are several uses for this. I am only going to go into one.
这有多种用途。我只会进入一个。
USE CASE: You are writing an application for web browsers. You want to write ES6 and have it transpiled to ES5.
用例：您正在为 Web 浏览器编写应用程序。您想编写 ES6 并将其转换为 ES5。
This is one of the use cases of --allowJs. In a sense, it will do everything that the TypeScript compiler does except type check your code.
这是 的用例之一--allowJs。从某种意义上说，它会做 TypeScript 编译器所做的一切，除了类型检查你的代码。
Without --allowJSthis would throw an error:
没有--allowJS这个会抛出一个错误：
var foo = {};
foo.name = "bar";
This is because the type literal {}does not have a property name. This is valid JavaScript -- and therefore would not trip up the compiler with the type checking turned off.
这是因为类型文字{}没有属性name。这是有效的 JavaScript —— 因此不会在类型检查关闭的情况下绊倒编译器。
If you did want to use type checking you would refactor it to:
如果您确实想使用类型检查，您可以将其重构为：
var foo: any = {};
foo.name = "bar";
Or even better:
或者甚至更好：
var foo = {name: "bar"};
