[英]Convert Array to Map Typescript
我正在嘗試將以下數組轉換為 Map:
const arr = [
{ key: 'user1', value: { num: 0, letter: 'a' } },
{ key: 'user2', value: { num: 0, letter: 'b' } },
{ key: 'user3', value: { num: 0, letter: 'c' } },
];
到目前為止我所擁有的:
const arr = [
{ key: 'user1', value: { num: 0, letter: 'a' } },
{ key: 'user2', value: { num: 0, letter: 'b' } },
{ key: 'user3', value: { num: 0, letter: 'c' } },
];
const b = arr.map(obj => [obj.key, obj.value]);
const map = new Map<string, { num: number; letter: string }>(b);
console.log(map.get('user1'));
你知道這是否可以實現嗎?
PS:你可以在這里找到 Typescript 游樂場和我得到的錯誤
obj.key
是一個string
, obj.value
是一個{num: number, letter: string}
,所以如果你把它們組成一個數組( [obj.key, obj.value]
),那么你會得到一個Array<string | {num: number, letter: string}>
Array<string | {num: number, letter: string}>
.
您需要告訴 TypeScript 您正在創建一個特定的tuple ,正如 Map 構造函數所期望的那樣,而不是通用數組。 有幾種方法可以做到這一點:
// The simplest: Tell TypeScript "I mean exactly what I said."
// (This makes it readonly, which isn't always desirable.)
const b = arr.map(obj => [obj.key, obj.value] as const);
// Or be explicit in a return type. You can do this at a few levels.
const b = arr.map<[string, { num: number, letter: string}]>(obj => [obj.key, obj.value]);
const b = arr.map((obj): [string, { num: number, letter: string}] => [obj.key, obj.value]);
// Or, as explained in the comments, do it in one line, and TypeScript
// can infer tuple vs. array itself.
const map = new Map(arr.map(obj => [obj.key, obj.value]));
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