Type Alias Join<Items, Delimiter>

Join: Items extends []
    ? ""
    : Items extends readonly [JoinableItem?]
        ? `${NullishCoalesce<Items[0], "">}`
        : Items extends readonly [
            infer First extends JoinableItem,
            ...(infer Tail extends readonly JoinableItem[]),
        ]
            ? `${NullishCoalesce<First, "">}${Delimiter}${Join<Tail, Delimiter>}`
            : Items extends readonly [
                ...(infer Head extends readonly JoinableItem[]),
                infer Last extends JoinableItem,
            ]
                ? `${Join<Head, Delimiter>}${Delimiter}${NullishCoalesce<Last, "">}`
                : string

Join an array of strings and/or numbers using the given string as a delimiter.

Use-case: Defining key paths in a nested object. For example, for dot-notation fields in MongoDB queries.

Type Parameters

Items extends readonly JoinableItem[]
Delimiter extends string

Example

import type {Join} from 'type-fest';

// Mixed (strings & numbers) items; result is: 'foo.0.baz'
const path: Join<['foo', 0, 'baz'], '.'> = ['foo', 0, 'baz'].join('.');

// Only string items; result is: 'foo.bar.baz'
const path: Join<['foo', 'bar', 'baz'], '.'> = ['foo', 'bar', 'baz'].join('.');

// Only number items; result is: '1.2.3'
const path: Join<[1, 2, 3], '.'> = [1, 2, 3].join('.');

// Only bigint items; result is '1.2.3'
const path: Join<[1n, 2n, 3n], '.'> = [1n, 2n, 3n].join('.');

// Only boolean items; result is: 'true.false.true'
const path: Join<[true, false, true], '.'> = [true, false, true].join('.');

// Contains nullish items; result is: 'foo..baz..xyz'
const path: Join<['foo', undefined, 'baz', null, 'xyz'], '.'> = ['foo', undefined, 'baz', null, 'xyz'].join('.');

// Partial tuple shapes (rest param last); result is: `prefix.${string}`
const path: Join<['prefix', ...string[]], '.'> = ['prefix'].join('.');

// Partial tuple shapes (rest param first); result is: `${string}.suffix`
const path: Join<[...string[], 'suffix'], '.'> = ['suffix'].join('.');

// Tuples items with nullish unions; result is '.' | 'hello.' | '.world' | 'hello.world'
const path: Join<['hello' | undefined, 'world' | null], '.'> = ['hello', 'world'].join('.');

Type Alias Join<Items, Delimiter>

Type Parameters

Example

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