javascript - 如何在 typescript 中减去两个只读数组

Question

我们知道我们不能在 Typescript 中连接只读数组，
但是我们可以做到这一点

readonly ArrA = [1, 2, 3] as const;
readonly ArrB = [4, 5] as const;
readonly Arr = [...ArrA, ...ArrB];

那么加法就完成了，减法呢？
ps:如果不是readonly，我们可以这样做

ArrA.filter(n => !ArrB.includes(n));

Answer 1

includes如果将“ES7”添加到 compilerOptions.lib，将可用(无论是否为只读)在 tsconfig.json .

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如果你关心数组成员级别的类型安全，你可以这样做:

const ArrA = [1, 2, 3] as const;
const ArrB = [3, 4, 5] as const;

// Aliases for tuple-member types
type ArrAMember = typeof ArrA[number] // (1 | 2 | 3)
type ArrBMember = typeof ArrB[number] // (3 | 4 | 5)

type ExclusionListMember = Exclude<ArrAMember, ArrBMember> // (1 | 2)

// Type-guard to verify exclusion
function isExcludedByB(i: ArrAMember): i is ExclusionListMember {
    return !ArrB.includes(i as any)
}

const ArrC = ArrA.filter(isExcludedByB)
//    ^ (1 | 2)[]