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Array FlatMap

Suprabha
🔥 New JS, CSS, HTML articles every week 🔥 Frontend engineer @gojekindonesia 👩🏻‍💻 http://instagram.com/suprabhasupi
・1 min read

FlatMap is a single method which can be usable for flat and map methods.

As you know flat(), flattening the 1-level deep and map() to loop into an array.

If we include both, we called flatMap() 😉

So, instead if calling two methods flat() and map(), you can use single method called flatMap().

let plants = ['💐', '🌲', '🌻', '🌹'];

// ❌ map + flat
plants.map(plant => [plant, '🍁']).flat();
// Output
//["💐", "🍁", "🌲", "🍁", "🌻", "🍁", "🌹", "🍁"]

// ✅ flatMap
plants.flatMap(plant => [plant, "🍁"])

// Output
// ["💐", "🍁", "🌲", "🍁", "🌻", "🍁", "🌹", "🍁"]
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How flatMap() works?

📝 FlatMap() always do first map() and then it flat().

In flat(), we use to pass arguments where you set the depth, arguments define how deep a nested array should be flattened.

let plants = [[["🌻", "🌹"]]];
plants.flat(2);

// ["🌻", "🌹"]
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flatMap() do only 1 level deep flattening.

let plants = [[["🌻", "🌹"]]];
plants.flatMap(plant => [plant]);

// [["🌻", "🌹"]]
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Filter using flatMap 😉

Yes, You can also do filter here using flatMap().

let arr = [5, 4, -3, 20, -4, 18]
arr.flatMap(i => {
  return i < 0 ? [] : [i];
})

// [5, 4, 20, 18]
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Reference 🧐

Summary ∑

flatMap() method always helps if you want to use map and flat methods both together.

Thanks for reading the article ❤️

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Discussion (1)

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ayabouchiha profile image
Aya Bouchiha

Thank you!