Javascript: How to replace first object's values with values from second object, if objects have matching keys

Question

I have 2 js objects:

var date_dict = {2017_M1: 0, 2017_M10: 0, 2017_M11: 0}
var data_dict = {2017_M1: 10,  2017_M11: 50}

Expected output = {2017_M1: 10, 2017_M10: 0, 2017_M11: 50}

Aim: To map the values of data_dict (target) to date_dict (source) where they exist. Keep all keys of date_dict (source). Keep values of date_dict if not exist in data_dict.

There will never be any keys in data_dict that do not exist in date_dict (this is universe of dates).

I've tried, based on switching key/value an answer to How to replace object key with matching key value from another object

Below attempt just returns the date_dict, it doesn't get the data_dict values.

Thanks :

var expected_output = Object.fromEntries(
                Object.entries(date_dict).map(([k,v]) => [ k, (data_dict[v] || v)])

do you want to keep the same object?

Nina Scholz
– Nina Scholz

2020-09-15 17:52:31 +00:00
Commented Sep 15, 2020 at 17:52 — Nina Scholz
– Nina Scholz, Commented Sep 15, 2020 at 17:52
Console.log({ ...obj1, ...obj2 }) ?

quirimmo
– quirimmo

2020-09-15 17:52:48 +00:00
Commented Sep 15, 2020 at 17:52 — quirimmo
– quirimmo, Commented Sep 15, 2020 at 17:52

Jacob · Accepted Answer · 2020-09-15 17:51:47Z

5

You can use the spread operator for this:

const expected_output = {
  ...date_dict,
  ...data_dict
};

answered Sep 15, 2020 at 17:51

Jacob

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