(_.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; } 

Answer 2

You can simply filter out the keys with undefined values before passing them to Object.assign():

const assign = (target, ...sources) =>    Object.assign(target, ...sources.map(x =>      Object.entries(x)        .filter(([key, value]) => value !== undefined)        .reduce((obj, [key, value]) => (obj[key] = value, obj), {})    ))    console.log(assign({}, {key: 2}, {key: undefined}))