locutus/esm/elixir/Enum/scan.js

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

function isScanReducer(value) {
    return typeof value === 'function';
}
export function scan(values, initialOrReducer, maybeReducer) {
    //      discuss at: https://locutus.io/elixir/scan/
    // parity verified: Elixir 1.18
    //     original by: Kevin van Zonneveld (https://kvz.io)
    //          note 1: Produces running accumulator states, similar to Elixir Enum.scan/2 and Enum.scan/3.
    //       example 1: scan([1, 2, 3, 4], (acc, value) => Number(acc) + Number(value))
    //       returns 1: [1, 3, 6, 10]
    //       example 2: scan([1, 2, 3], 10, (acc, value) => Number(acc) + Number(value))
    //       returns 2: [11, 13, 16]
    //       example 3: scan([], 5, (acc, value) => Number(acc) + Number(value))
    //       returns 3: []
    if (!Array.isArray(values)) {
        return [];
    }
    const hasInitial = typeof maybeReducer === 'function';
    if (values.length === 0) {
        return [];
    }
    const out = [];
    if (hasInitial) {
        const reducer = maybeReducer;
        if (!isScanReducer(reducer)) {
            throw new TypeError('scan(): reducer must be a function');
        }
        let accumulator = initialOrReducer;
        for (let i = 0; i < values.length; i++) {
            accumulator = reducer(accumulator, values[i], i, values);
            out.push(accumulator);
        }
        return out;
    }
    if (!isScanReducer(initialOrReducer)) {
        throw new TypeError('scan(): reducer must be a function');
    }
    const reducer = initialOrReducer;
    let accumulator = values[0];
    out.push(accumulator);
    for (let i = 1; i < values.length; i++) {
        accumulator = reducer(accumulator, values[i], i, values);
        out.push(accumulator);
    }
    return out;
}