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Include null and undefined elements in flat() example #36095

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Sep 29, 2024
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Include null and undefined elements in flat() example #36095

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2089d21
Include null and undefined elements in flat() examples
DanKaplanSES Sep 29, 2024
d26ed52
In flat() docs, change "ignore empty slots" to "remove empty slots"
DanKaplanSES Sep 29, 2024
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10 changes: 5 additions & 5 deletions files/en-us/web/javascript/reference/global_objects/array/flat/index.md
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Expand Up @@ -33,7 +33,7 @@ A new array with the sub-array elements concatenated into it.

The `flat()` method is a [copying method](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array#copying_methods_and_mutating_methods). It does not alter `this` but instead returns a [shallow copy](/en-US/docs/Glossary/Shallow_copy) that contains the same elements as the ones from the original array.

The `flat()` method ignores empty slots if the array being flattened is [sparse](/en-US/docs/Web/JavaScript/Guide/Indexed_collections#sparse_arrays). For example, if `depth` is 1, both empty slots in the root array and in the first level of nested arrays are ignored, but empty slots in further nested arrays are preserved with the arrays themselves.
The `flat()` method removes empty slots if the array being flattened is [sparse](/en-US/docs/Web/JavaScript/Guide/Indexed_collections#sparse_arrays). For example, if `depth` is 1, both empty slots in the root array and in the first level of nested arrays are ignored, but empty slots in further nested arrays are preserved with the arrays themselves.

The `flat()` method is [generic](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array#generic_array_methods). It only expects the `this` value to have a `length` property and integer-keyed properties. However, its elements must be arrays if they are to be flattened.

Expand Down Expand Up @@ -61,7 +61,7 @@ arr4.flat(Infinity);

### Using flat() on sparse arrays

The `flat()` method removes empty slots in arrays:
The `flat()` method removes [empty slots](/en-US/docs/Web/JavaScript/Guide/Indexed_collections#sparse_arrays) in arrays:

```js
const arr5 = [1, 2, , 4, 5];
Expand All @@ -70,9 +70,9 @@ console.log(arr5.flat()); // [1, 2, 4, 5]
const array = [1, , 3, ["a", , "c"]];
console.log(array.flat()); // [ 1, 3, "a", "c" ]

const array2 = [1, , 3, ["a", , ["d", , "e"]]];
console.log(array2.flat()); // [ 1, 3, "a", ["d", empty, "e"] ]
console.log(array2.flat(2)); // [ 1, 3, "a", "d", "e"]
const array2 = [1, , 3, undefined, ["a", , ["d", , "e"]], null];
console.log(array2.flat()); // [ 1, 3, undefined, "a", ["d", empty, "e"], null ]
console.log(array2.flat(2)); // [ 1, 3, undefined, "a", "d", "e", null ]
```

### Calling flat() on non-array objects
Expand Down