How do I overwrite property if exists?

Question

Say I have object as follows:

let newObject = {
 foo: 'foo-value',
 bar: 'bar-value', 
 baz: 'baz-value'
};

I have also a list:

let list = ['foo', 'baz']

I want to overwrite 'foo-value' and 'baz-value' (value of keys that appear in the list) with some 'default-value'. So I have:

{
 foo: 'default-value',
 bar: 'bar-value', 
 baz: 'default-value'
};

If I have a different object, let's say

let differentObject = {
 x: 'x-value',
 y: 'y-value'
}

I don't want to add any default value so spread operator didn't work for me.

What have you tried so far to solve this on your own? – Andreas Mar 01 '22 at 10:26 — Andreas, Mar 01 '22 at 10:26
Where do you get the "default-value"? – Andreas Mar 01 '22 at 10:27 — Andreas, Mar 01 '22 at 10:27
`list.forEach(k => obj[k] = 'default-value');` – 0stone0 Mar 01 '22 at 10:27 — 0stone0, Mar 01 '22 at 10:27

score 0 · Accepted Answer · edited Mar 01 '22 at 10:29

0

You can achieve that like this

let newObject = {
 foo: 'foo-value',
 bar: 'bar-value', 
 baz: 'baz-value'
};

let list = ['foo', 'baz'];

list.forEach(item => {
  if(newObject[item])
   newObject[item] = 'Default value';
})

console.log(newObject);

edited Mar 01 '22 at 10:29

0stone0

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answered Mar 01 '22 at 10:28

sazzad

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Where is the check that the property exists? I only see a check that the resolved property value is truthy. This is also problematic because it creates new properties if they were only inherited before. – Sebastian Simon Mar 01 '22 at 11:05
@SebastianSimon `if(newObject[item])` checks both of them – sazzad Mar 01 '22 at 11:08
So it’s not what is being asked for, then. This simply _fails_ for ``let newObject = { foo: "", bar: 0, baz: false }; Object.prototype.inherited = "this property does not exist on `newObject`."; let list = [ "foo", "bar", "baz", "inherited" ];``. – Sebastian Simon Mar 01 '22 at 11:14

How do I overwrite property if exists?

1 Answers1