locutus/ruby/Array/slice_when.js

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

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.slice_when = slice_when;
function slice_when(arr, boundary) {
    //      discuss at: https://locutus.io/ruby/Array/slice_when/
    // parity verified: Ruby 3.3
    //     original by: Kevin van Zonneveld (https://kvz.io)
    //          note 1: Starts a new slice whenever boundary(previous, current) returns true.
    //          note 2: Mirrors Ruby's Enumerable#slice_when behavior on arrays.
    //       example 1: slice_when([1, 2, 4, 5, 7, 8], (prev, curr) => curr - prev !== 1)
    //       returns 1: [[1, 2], [4, 5], [7, 8]]
    //       example 2: slice_when(['a', 'ab', 'abc', 'd', 'de'], (prev, curr) => curr.length <= prev.length)
    //       returns 2: [['a', 'ab', 'abc'], ['d', 'de']]
    //       example 3: slice_when([], () => true)
    //       returns 3: []
    if (!Array.isArray(arr) || arr.length === 0 || typeof boundary !== 'function') {
        return [];
    }
    const source = arr;
    const out = [[source[0]]];
    for (let i = 1; i < source.length; i++) {
        const previous = source[i - 1];
        const current = source[i];
        const shouldSlice = Boolean(boundary(previous, current, i, source));
        if (shouldSlice) {
            out.push([current]);
            continue;
        }
        const last = out.at(-1);
        if (last) {
            last.push(current);
        }
    }
    return out;
}