How to exclude a certain key of an object when mapping it? [duplicate]

Question

If I have an object, such as,

const obj = {
  a: 1,
  b: 2,
  c: 3,
}

I can map the keys and values as,

Object.entries(obj).map(([key, value]) => console.log(`${key}: ${value}`))

Is it possible in Javascript to omit a property, when mapping it?

Something like,

Object.entries({a: obj.a, ...obj}).map(([key, value]) => console.log(`${key}: ${value}`))

I can do the following:

Object.entries(obj).map(([key, value]) => key !== 'a' && console.log(`${key}: ${value}`))

But I feel like there can be a cleaner way to do this, and also this wouldn't work, because that mapped index will contain undefined. Just looking to clarify this.

Why are you using .map() here in the first place? You're not returning anything. Seems like you are using it as a .forEach(). — Ivar
– Ivar, Commented Jul 22, 2020 at 14:15
If you want to skip properties I'd just chain a .filter() and then a .map() — Anthony
– Anthony, Commented Jul 22, 2020 at 14:16
I'm mapping an object to JSX elements, and I need to exclude a specific key from a form data object. — Mike K
– Mike K, Commented Jul 22, 2020 at 14:16
@MikeK If you're mapping to jsx elements, then please show us the actual code that does that. — Bergi
– Bergi, Commented Jul 22, 2020 at 14:22
Perhaps useful is const filterMap = (f, m) => (xs) => xs .flatMap ((x) => f (x) ? [m (x)] : []) — Scott Sauyet
– Scott Sauyet, Commented Jul 22, 2020 at 14:40

adz5A · Accepted Answer · 2020-07-22 14:16:25Z

3

you can use filter

Object.entries(obj).filter(([key, _]) => key !== "a").map();

answered Jul 22, 2020 at 14:16

adz5A

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2 Comments

Filipe Pinheiro Over a year ago

You can use reduce after the filter to get an object back from the entries array. Object.entries(obj).filter(([key, _]) => key !== "a").reduce((res, [key, value]) => ({ ...res, [key]: value}), {});

Bergi Over a year ago

@FilipePinheiro OP doesn't want that? And no, you shouldn't use reduce for that, just call Object.fromEntries :-)

soltex · Accepted Answer · 2020-07-22 14:20:53Z

3

If you want to hide/exclude a key when using a map you can set its enumerable property to false, using Object.defineProperty:

const obj = {
  a: 1,
  b: 2,
  c: 3,
}

// this will hide key 'b' from obj
Object.defineProperty(obj, 'b', {
  enumerable: false,  
});

Object.entries(obj).map(([key, value]) => console.log(`${key}: ${value}`))

answered Jul 22, 2020 at 14:20

soltex

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Comments

8HoLoN · Accepted Answer · 2020-07-22 14:18:16Z

2

Here is what you want:

const obj = {
    a: 1,
    b: 2,
    c: 3,
}


const res = Object.entries(obj).filter(([key, value]) => key !== 'a');

console.log(res);

answered Jul 22, 2020 at 14:18

8HoLoN

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