https://www.karltarvas.com/2021/03/11/typescript-array-filter-boolean.html
对于 Array.filter(Boolean) 这种过滤数组的方法，Typescript 却并没有天然地支持它。《a lot of history to this issue》(https://github.com/microsoft/TypeScript/issues/16655) 帖子中提及了这个问题，且至今没有被完全修复。
在下面的代码片段中，filter 后的返回值 理应 是 string[]，但实际得到的却是 (string | null | undefined)[]。
const foo: (string | null | undefined)[] = [];
const bar: string[] = foo.filter(Boolean);
// ^^^
// Type '(string | null | undefined)[]' is not assignable to type 'string[]'.要修正该问题，可以为 Array.prototype.filter() 增加一个 TS overload，以应对用布尔值构造函数作为过滤函数时的特殊情况。将下列代码保存为 lib.es5.d.ts:
/**
* Fixes https://github.com/microsoft/TypeScript/issues/16655 for `Array.prototype.filter()`
* For example, using the fix the type of `bar` is `string[]` in the below snippet as it should be.
*
* const foo: (string | null | undefined)[] = [];
* const bar = foo.filter(Boolean);
*
* For related definitions, see https://github.com/microsoft/TypeScript/blob/master/src/lib/es5.d.ts
*
* Original licenses apply, see
* - https://github.com/microsoft/TypeScript/blob/master/LICENSE.txt
* - https://stackoverflow.com/help/licensing
*/
/** See https://stackoverflow.com/a/51390763/1470607 */
type Falsy = false | 0 | "" | null | undefined;
interface Array<T> {
/**
* Returns the elements of an array that meet the condition specified in a callback function.
* @param predicate A function that accepts up to three arguments. The filter method calls the predicate function one time for each element in the array.
* @param thisArg An object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.
*/
filter<S extends T>(predicate: BooleanConstructor, thisArg?: any): Exclude<S, Falsy>[];
}然后将其作为 include 项添加到 tsconfig 配置中即可：
{
"include": [
"lib.es5.d.ts"
]
}
