CODEWITHSUNDEEP
javascripttypescript
methuselah
methuselah

Reputation: 13206

Object array returns undefined after filter is run on it

I have an array with the following structure

let pageComponents = { pages: [ { "components": [ ... ] }, { "components": [ ... ] } ] };

See Remove null entries from array of objects for the contents of components.

I've tried to run the following filter method on it, but the object array returns null afterwards. Any idea on how I can fix it?

  static deleteEmptyComponentsOnMultiplePages(components) {
    return components['pages'].forEach(obj => {
        obj['components'].filter(item => item !== null);
      }
    );
  }

Upvotes: 0

Views: 58

Answers (2)

Rohit.007
Rohit.007

Reputation: 3502

ForEach is iterator only and its return type is void. you need to use other iterator methods like map

let pageComponents = {
  pages: [
  {
    "components": [1, 2, 4, null]
  }, 
  {
    "components": ['a', 'b', null, 'd']
  }
  ]
};

function deleteEmptyComponentsOnMultiplePages(components) {
    return components.map(obj => {
        return obj.components.filter(item => item !== null);
    });
}

console.log(deleteEmptyComponentsOnMultiplePages(pageComponents.pages))

Upvotes: 0

Maheer Ali
Maheer Ali

Reputation: 36564

forEach doesn't return anything it just loops. Here you need to use map().

You also need to use return inside the callback of map() otherwise you will get an array of undefined

static deleteEmptyComponentsOnMultiplePages(components) {
    return components['pages'].map(obj => {
        return obj['components'].filter(item => item !== null);
    });
}

You can exclude {} of map() and return implicitly

static deleteEmptyComponentsOnMultiplePages(components) {
    return components['pages'].map(obj => obj['components'].filter(item => item !== null));
}

You can use destructuring for more cleaner code

static deleteEmptyComponentsOnMultiplePages({pages}) {
    return pages.map(({components}) => components.filter(item => item !== null));
}

Upvotes: 5

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