(_.merge in ES6/ES7)Object.assign without overriding undefined values

Question

There is _.merge functionality in lodash. I want to achieve the same thing in ES6 or ES7.

Having this snippet:

Object.assign({}, {key: 2}, {key: undefined})

I want to receive {key: 2}. Currently I receive {key: undefined}

This is NOT a deep merge.

Is it possible? If yes then how to achieve that?

Answer 1

You can't achieve that with a straight usage of Object.assign, because each next object will rewrite the same keys for prev merge. The only way, to filter your incoming objects with some hand-crafted function.

function filterObject(obj) {
    const ret = {};
    Object.keys(obj)
        .filter((key) => obj[key] !== undefined)
        .forEach((key) => ret[key] = obj[key]);
    return ret;
}