shelving/util/merge.js

Toolkit for using data in JavaScript.

import { isArray, withArrayItems } from "./array.js";
import { isObject } from "./object.js";
// Internal shared by shallow/deep merge.
function _merge(left, right, recursor) {
    if (left === right)
        return right;
    if (isArray(right))
        return isArray(left) ? mergeArray(left, right) : right;
    if (isObject(right))
        return isObject(left) && !isArray(left) ? mergeObject(left, right, recursor) : right;
    return right;
}
/**
 * Exact merge two unknown values.
 * - Always returns `right`.
 */
export function exactMerge(left, right) {
    return right;
}
export function shallowMerge(left, right) {
    return _merge(left, right, exactMerge);
}
export function deepMerge(left, right) {
    return _merge(left, right, deepMerge);
}
export function mergeArray(left, right) {
    if (left === right)
        return right;
    if (!right.length)
        return left;
    if (!left.length)
        return right;
    return withArrayItems(left, ...right);
}
export function mergeObject(left, right, recursor = exactMerge) {
    if (left === right)
        return right;
    // If `right` has no keys then merge result will always be `left` (because there's nothing to merge).
    const rightEntries = Object.entries(right);
    if (!rightEntries.length)
        return left;
    const leftKeys = Object.keys(left);
    const merged = { ...left };
    let changed = false;
    for (const [k, r] of rightEntries) {
        if (leftKeys.includes(k)) {
            if (r === undefined) {
                changed = true; // Literal `undefined` means "delete this prop"
            }
            else {
                const l = left[k];
                const m = recursor(l, r);
                if (m !== l) {
                    changed = true;
                    merged[k] = m;
                }
            }
        }
        else {
            changed = true;
            if (r !== undefined)
                merged[k] = r;
        }
    }
    return changed ? merged : left;
}