如何在typescript中定义const数组

Question

我的代码:

const WEEKDAYS_SHORT: string[] = ['Dim', 'Lun', 'Mar', 'Mer', 'Jeu', 'Ven', 'Sam']

错误消息来自TypeScript(3.0)编译器:

TS2322:类型'string []'不能赋值为'[string,string,string,string,string,string,string]'.'string []'类型中缺少属性'0'.

如果我更改string[]为ReadonlyArray<string>,则错误消息变为:

TS2322:类型'ReadonlyArray'不能赋值为'[string,string,string,string,string,string,string]'.'ReadonlyArray'类型中缺少属性'0'.

我的tsconfig.json:

{
  "compilerOptions": {
    "declaration": false,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "lib": ["es6", "dom"],
    "module": "es6",
    "moduleResolution": "node",
    "sourceMap": true,
    "target": "es5",
    "jsx": "react",
    "strict": true
  },
  "exclude": [
    "**/*.spec.ts",
    "node_modules",
    "vendor",
    "public"
  ],
  "compileOnSave": false
}

如何在TypeScript中定义只读数组？

Answer 1

You may add as const to your declaration;

const readonlyArray = [1, 2, 3] as const;

Furthermore the type typeof readonlyArray[number] would be 1 | 2 | 3

Answer 2

正如您所指出的，问题的原因是您尝试将字符串数组 ( string[]) 分配给 7 字符串元组。虽然您要使用的解决方案any可行，但通常不建议使用any. 拼写出柔顺也不太理想，因为它太长了。

我们可以做的是创建一个辅助函数来创建元组类型。该函数可在任何需要元组的地方重用：

function tupleArray<T extends any[]>(...v: T) {
    return v;
}
const WEEKDAYS_SHORT_INFFERED =  tupleArray('Dim', 'Lun', 'Mar', 'Mer', 'Jeu', 'Ven', 'Sam')  // INFFERED AS [string, string, string, string, string, string, string]
const WEEKDAYS_SHORT: [string, string, string, string, string, string, string] = WEEKDAYS_SHORT_INFFERED