locutus/esm/clojure/core/merge_with.js

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

export function merge_with(combiner, ...maps) {
    //      discuss at: https://locutus.io/clojure/merge_with/
    // parity verified: Clojure 1.12
    //     original by: Kevin van Zonneveld (https://kvz.io)
    //          note 1: Merges maps and combines colliding values with combiner, like Clojure merge-with.
    //       example 1: merge_with((a, b) => Number(a) + Number(b), {a: 1}, {a: 2, b: 3})
    //       returns 1: {a: 3, b: 3}
    //       example 2: merge_with((a, b) => [a, b].join(','), {x: 'a'}, {x: 'b'}, {y: 'c'})
    //       returns 2: {x: 'a,b', y: 'c'}
    //       example 3: merge_with((a, b) => b, {})
    //       returns 3: {}
    if (typeof combiner !== 'function') {
        throw new TypeError('merge_with(): combiner must be a function');
    }
    const out = {};
    for (const map of maps) {
        if (!map || typeof map !== 'object' || Array.isArray(map)) {
            continue;
        }
        for (const [key, value] of Object.entries(map)) {
            if (Object.hasOwn(out, key)) {
                out[key] = combiner(out[key], value, key);
            }
            else {
                out[key] = value;
            }
        }
    }
    return out;
}