1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
|
// @strictNullChecks: true
type Narrowable = string | number | bigint | boolean;
type Narrow<A> = (A extends Narrowable ? A : never) | ({
[K in keyof A]: Narrow<A[K]>;
});
const satisfies =
<TWide,>() =>
<TNarrow extends TWide>(narrow: Narrow<TNarrow>) =>
narrow;
/* ========================================================================== */
const isNotNull = <T,>(value: T | null): value is T => value !== null;
type Item = { value: string | null };
const item1 = satisfies<Item>()({ value: "1" });
const item2 = satisfies<Item>()({ value: "2" });
const item3 = satisfies<Item>()({ value: null });
const values2: Array<"1" | "2" | null> = ["1", "2", null];
const filteredValues2 = values2.filter(isNotNull);
const values1 = [item1, item2, item3].map(item => item.value);
const filteredValues1 = values1.filter(isNotNull);
|
