Defaults with nested object

Question

Suppose I have the following object which provides the default value:

default_values = {a: 0, b: 0, c: {aa: 0, bb: 0}}

I also have another object that would override some of these default values:

override_values = {a: 5, c: {aa: 5}}

What I'd like to have is to combine these two objects that would result in

combined: {a: 5, b: 0, c: {aa: 5, bb: 0}}

However, using the regular spread operator like {...default_values, ...override_values} would just give c: {aa: 5} instead of c: {aa: 5, bb: 0}. The object could be huge so I can't hard-code all the nested objects.

I could write a function to basically go over each key... if the value is not an object then use override | default, otherwise recursively call this function on the nested object. But I feel like this is very common that there's already something like this.

Answer 1

You're looking for something along the lines of deep_merge or merge. These functions are widely and are presented in lodash library.

Here is an example of it:-

function merge(target, source) {
  Object.keys(source).forEach(key => {
    const sourceValue = source[key];
    if (sourceValue) {
      const targetValue = target[key];
      const newValues = merge(targetValue, sourceValue);
      Object.assign(sourceValue, newValues);
    }
  });

  Object.assign(target || {}, source);
  return target;
}