flattenDeep()

flattenDeep<T>(array): T[]

Recursively flattens array.

DEPRECATED

Use array.flat(Infinity) directly instead.

Reason:
Native equivalent method now available

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Type Parameters

T: T

The type of the leaf elements in the array.

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Parameters

array: unknown[]

The array to flatten.

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Returns: T[]

A new deeply flattened array.

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See Also

• Array.flat() - MDN
• Browser support - Can I Use

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Since

2.0.0

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Also known as

flat (Radashi) · flatten (Ramda) · flattenDeep (Lodash, es-toolkit, Remeda) · ❌ (Effect, Modern Dash, Antfu)

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Example

const deeplyNested = [1, [2, [3, [4, [5]]]]];

// ❌ Deprecated approach
const flattened = flattenDeep(deeplyNested);
console.log(flattened); // [1, 2, 3, 4, 5]

// ✅ Recommended approach
const flattenedNative = deeplyNested.flat(Infinity);
console.log(flattenedNative); // [1, 2, 3, 4, 5]

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How it works?

Recursively flattens an array to a single level. Deprecated: Use array.flat(Infinity) directly.

Deep Recursion

Native Equivalent

// ❌ flattenDeep(arr)
// ✅ arr.flat(Infinity)

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Use Cases

Flatten deeply nested structures 📌

Flatten all levels of nesting in arrays.

#flatten#deep#nested#recursive

const nested = [1, [2, [3, [4, [5]]]]];
nested.flat(Infinity);
// => [1, 2, 3, 4, 5]

Normalize tree data

Extract all items from a tree structure.

#normalize#tree#data#hierarchy

const tree = [node1, [node2, [node3, node4]]];
tree.flat(Infinity);
// => [node1, node2, node3, node4]

Collect all leaf values

Get all leaf values from nested data.

#collect#leaf#values#recursive

const data = [[a, [b, c]], [[d], e]];
data.flat(Infinity);
// => [a, b, c, d, e]