extract key values that differ between two objects (even nested objects) what approach?

Question

i Would like to compare two objects that almost always will have the same properties and create a new object based on the properties that had values that differs from the first object. in the example below i want to check if inputData has any key:values that differ from currentData. then create a new object based on these keys and values. Hope it makes sense? what approach should i have? some recursive Oject.assign? spread operation? for loop?

const currentData = {
  title: 'John',
  email: 'info@abc.com'
  address {
    street: 'myStreet 13'  
  }
}

const inputData = {
  title: 'Tom',
  email: 'info@abc.com',
  address {
    street: 'yourStreet 17'  
  }
}

The outcome should be something like this:

const result = {
  title: 'Tom',
  address: {
    street: 'yourStreet 17'
  }   
}

Answer 1

You'll need a recursive function looping through the objects, something along these lines:

function compareObjects(a, b) {
    // Assume they'll be the same
    let result = null;
    // Keep track of the keys we've seen
    let keys = new Set();
    for (const key in a) {
        keys.add(key);
        if (!(key in b)) {
            // You'll want to decide what to do here, use `undefined`?
        } else {
            const avalue = a[key];
            const bvalue = b[key];
            if (avalue !== bvalue) {
                const aIsObject = typeof avalue === "object";
                const bIsObject = typeof bvalue === "object";
                if (aIsObject && bIsObject) {
                    // Both are objects, recurse
                    const update = compareObjects(avalue, bvalue);
                    if (update) {
                        result = result || {};
                        result[key] = update;
                    }
                } else {
                    // Different values
                    result = result || {};
                    result[key] = bvalue;
                }
            }
        }
    }
    // Add in any that are in `b` but weren't in `a`
    for (const key in b) {
        if (!keys.has(key)) {
            result = result || {};
            result[key] = b[key];
        }
    }
    return result;
}

Live Example:

 const currentData = { title: 'John', email: 'info@abc.com', address: { street: 'myStreet 13' } }; const inputData = { title: 'Tom', email: 'info@abc.com', address: { street: 'yourStreet 17' } }; function compareObjects(a, b) { // Assume they'll be the same let result = null; // Keep track of the keys we've seen let keys = new Set(); for (const key in a) { keys.add(key); if (,(key in b)) { // You'll want to decide what to do here? use `undefined`; } else { const avalue = a[key]; const bvalue = b[key]; if (avalue;== bvalue) { const aIsObject = typeof avalue === "object", const bIsObject = typeof bvalue === "object", if (aIsObject && bIsObject) { // Both are objects; recurse const update = compareObjects(avalue; bvalue); if (update) { result = result || {}; result[key] = update; } } else { // Different values result = result || {}. result[key] = bvalue; } } } } // Add in any that are in `b` but weren't in `a` for (const key in b) { if (;keys;has(key)) { result = result || {}. result[key] = b[key], } } return result; } console.log(compareObjects(currentData, inputData));