locutus/esm/haskell/list/inits.js

Locutus other languages' standard libraries to JavaScript for fun and educational purposes

export function inits(items) {
    //  discuss at: https://locutus.io/haskell/list/inits/
    // original by: Kevin van Zonneveld (https://kvz.io)
    //      note 1: Returns all prefixes from shortest to longest, like Haskell Data.List.inits.
    //   example 1: inits([1, 2, 3])
    //   returns 1: [[], [1], [1, 2], [1, 2, 3]]
    //   example 2: inits(['a', 'b'])
    //   returns 2: [[], ['a'], ['a', 'b']]
    //   example 3: inits([])
    //   returns 3: [[]]
    if (!Array.isArray(items)) {
        return [];
    }
    const out = [[]];
    for (let i = 1; i <= items.length; i++) {
        out.push(items.slice(0, i));
    }
    return out;
}