typescript 运行时未定义枚举类型
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Enum type not defined at runtime
提问by Thijs Koerselman
I have a problem where the Typescript compiler compiles my code successfully, yet the runtime gives me undefined type errors.
我有一个问题，Typescript 编译器成功编译了我的代码，但运行时却给了我未定义的类型错误。
In my app I created a types.tsfile with some things shared between multiple other ts files. It contains a string enum like:
在我的应用程序中，我创建了一个types.ts文件，其中包含在多个其他 ts 文件之间共享的一些内容。它包含一个字符串枚举，如：
enum MyEnum {
One = "one";
Two = "two";
}
When I define it like this. The compiler lets me use it in other ts files, and appears to be happy. However, at runtime I get the error "MyEnum is not defined".
当我这样定义它时。编译器让我在其他 ts 文件中使用它，看起来很高兴。但是，在运行时我收到错误“MyEnum 未定义”。
I know of two ways to solve this:
我知道有两种方法可以解决这个问题：
- Define the enum in the file where it is used. But I don't think this will solve anything for other files that want to use it.
- Use "export" in the types.ts file, and import every type explicitly everywhere it is used.
- 在使用它的文件中定义枚举。但我认为这不会为其他想要使用它的文件解决任何问题。
- 在 types.ts 文件中使用“export”，并在使用它的任何地方明确导入每种类型。
I am quite new to Typescript, and I feel I might be misunderstanding something fundamental.
我对打字稿很陌生，我觉得我可能误解了一些基本的东西。
First, I don't get why the Typescript compiler happily compiles my code if there's going to be a runtime error. I would understand it if I had used the declarekeyword, telling the compiler that something shouldbe available at runtime, but in this case I don't see why it should assume that the enum comes from anywhere else then the types.ts file.
首先，如果出现运行时错误，我不明白为什么 Typescript 编译器会愉快地编译我的代码。如果我使用了declare关键字，我会理解它，告诉编译器某些东西应该在运行时可用，但在这种情况下，我不明白为什么它应该假设枚举来自 types.ts 文件之外的任何其他地方。
Second, I would like to define types somewhere globally in my app and have them be available everywhere without having to import them every time I used them. How do I accomplish this? Or is this maybe considered bad practice?
其次，我想在我的应用程序中的某个地方全局定义类型，并让它们随处可用，而不必每次使用它们时都导入它们。我该如何实现？或者这可能被认为是不好的做法？
I am using Typescript 2.6 and my config looks like this:
我正在使用 Typescript 2.6，我的配置如下所示：
{
"compilerOptions": {
/* Basic Options */
"target": "es6",
"module": "commonjs",
"lib": ["es6", "es7", "esnext"],
"sourceMap": true /* Generates corresponding '.map' file. */,
"outDir": "build" /* Redirect output structure to the directory. */,
"removeComments": true /* Do not emit comments to output. */,
/* Strict Type-Checking Options */
"strict": true /* Enable all strict type-checking options. */,
/* Additional Checks */
"noUnusedLocals": true /* Report errors on unused locals. */,
"noUnusedParameters": true /* Report errors on unused parameters. */,
"noImplicitReturns": true /* Report error when not all code paths in function return a value. */,
"noFallthroughCasesInSwitch": true /* Report errors for fallthrough cases in switch statement. */,
"plugins": [{ "name": "tslint-language-service" }],
"skipLibCheck": true // because firebase-sdk has wrong type files now (Nov 18)
},
"include": ["src/**/*"],
"exclude": ["build"]
}
采纳答案by Matt B
There's another way you can do this. If you don't want to export your enum you can define it as a const enum
还有另一种方法可以做到这一点。如果您不想导出枚举，可以将其定义为const 枚举
const enum MyEnum {
One = "one";
Two = "two";
}
These are inlined by the compiler and are completely removed during compilation.
这些由编译器内联，并在编译期间完全删除。
回答by keos
In my case of undefinedenum, it turned out it's because of circular import:
在我的undefined枚举情况下，结果是因为循环导入：
export enum A {...}defined in file a.ts,
export const b = ...defined in file b.ts;
export enum A {...}在文件a.ts中export const b = ...定义，在文件中
定义b.ts；
import {A} from './a.ts'in b.ts,
while import {b} from './b.ts'in a.ts.
import {A} from './a.ts'在b.ts，而import {b} from './b.ts'在a.ts。
The error was gone after removing circular imports.
删除循环导入后错误消失了。
回答by Chintsu
I had the same problem when imported re-exported enum. It caused runtime error.
导入重新导出枚举时，我遇到了同样的问题。它导致运行时错误。
layout.ts
布局.ts
export enum Part { Column, Row }
index.ts
索引.ts
export * from './layout'
component.ts
组件.ts
import { Part } from '../entities' // This causes error
import { Part } from '../entities/layout' // This works
回答by Ciaran Gallagher
I had this error and it went away as soon as I used the export keyword, i.e.
我遇到了这个错误，一旦我使用了 export 关键字，它就消失了，即
export enum MyEnum {
One = "one";
Two = "two";
}
And make sure you import it in the files where you are using it as well, i.e.
并确保将它导入到您正在使用它的文件中，即
import { MyEnum } from '../types.ts';
I found that when I declared the enum without the export keyword, I could still reference the enum without importing it in other files without a compiler error - it was only at runtime the undefined exception was then thrown.
我发现，当我在没有 export 关键字的情况下声明枚举时，我仍然可以引用枚举，而无需将其导入到其他文件中，而不会出现编译器错误 - 只有在运行时才会抛出未定义的异常。
回答by Baki
For us it turned out that simply restarting the application solved the problem. (Nativescript app)
对我们来说，结果证明只需重新启动应用程序即可解决问题。（本机脚本应用程序）
回答by Ranjeet Kumar
export enum Expertlavel {
Beginner = 0,
Intermediate = 10,
Expert = 20
};
Exporting all enum classes
导出所有枚举类
export * from "../Enums/enums";
