JS Object diff function

objdiff.js

const objDiff = (a, b) => {
    if (typeof a === typeof b && typeof a === 'object') {
        const diff = {};
        let changed = false;
        for (let i in a) {
            if (!b.hasOwnProperty(i)) {
                diff[i] = 'DELETED';
                changed = true;
                continue;
            }
            const d = objDiff(a[i], b[i]);
            if (d !== undefined) {
                diff[i] = d;
                changed = true;
            }
        }
        for (let i in b) {
            if (!a.hasOwnProperty(i)) {
                diff[i] = b[i];
                changed = true;
            }
        }
        if (changed) return diff;
    } else if (a !== b) return b;
    return undefined;
};