Get and set deeply nested object properties via paths

pathfinder.js

const has = {}.hasOwnProperty;

function getPath(root, tester, path = []) {
    for (const key in root) {
        if (has.call(root, key)) {
            const value = root[key];
            if (tester(key, value) === true) {
                path.push(key);
                return path;
            }
            if (typeof value === 'object' && value !== null) {
                const copy = path.slice().concat([key]);
                const result = getPath(value, tester, copy);
                if (result) {
                    return result;
                }
            }
        }
    }
}

function setPath(root, path, value) {
    let obj = root;
    const copy = path.slice();
    while(obj && copy.length > 0) {
        const prop = copy.shift();
        if (copy.length === 0) {
            obj[prop]= value;
        } else {
            obj = obj[prop];
        }
    }
}

// Usage:

const obj = {
    a: {
        b: {
            c: 10,
            d: {
                e: 20
            }
        },
        f: {
            g: 30,
            h: 40,
            i: {
                j: 50
            },
            k: {
                l: {
                    m: 60
                }
            }
        },
        n: {
            o: 70
        }
    },
    p: {
        q: 80
    }
};

// Provide a test function to get the path to the first property that satisfies a condition
const path = getPath(obj, (key, val) => val === 60); //=> ["a", "f", "k", "l", "m"]

console.log(obj.a.f.k.l.m); //=> 60

// Set a new value for the property with the given path;
setPath(obj, path, 100);

console.log(obj.a.f.k.l.m); //=> 100