Array Methods

JavaScript · Methods reference

JavaScript · Methods reference

📋 Overview

All common Array prototype methods (ES2024). Prefer non-mutating toSorted/toReversed when state is shared.

🔧 Methods

Static

Method	Description
`Array.isArray(v)`	True for real arrays
`Array.from(iter, mapFn?)`	From iterable/array-like
`Array.fromAsync(asyncIter)`	Await async iterable (ES2024)
`Array.of(...items)`	Create from items (not length trap)

Mutating

Method	Description
`push(...items)` / `pop()`	End add/remove
`unshift(...items)` / `shift()`	Start add/remove — O(n)
`splice(start, deleteCount, ...items)`	Delete/insert; returns removed
`sort(compareFn?)`	In-place sort — default string order
`reverse()`	In-place reverse
`fill(value, start?, end?)`	Fill range
`copyWithin(target, start, end?)`	Copy slice within array

Non-mutating (ES2023+)

Method	Description
`toSorted(compareFn?)`	Sorted copy
`toReversed()`	Reversed copy
`toSpliced(start, deleteCount, ...items)`	Spliced copy
`with(index, value)`	Copy with one index replaced
`slice(start?, end?)`	Shallow subarray copy
`concat(...items)`	Concatenate into new array

Search & iterate

Method	Description
`at(index)`	Element at index (supports negative)
`includes(value, fromIndex?)`	SameValueZero membership
`indexOf` / `lastIndexOf`	Strict index or -1
`find` / `findLast`	First/last match by predicate
`findIndex` / `findLastIndex`	Index of match or -1
`some` / `every`	Any / all pass predicate
`forEach(fn)`	Side-effect iteration
`map` / `filter`	Transform / keep elements
`flat(depth?)` / `flatMap(fn)`	Flatten nested arrays
`reduce` / `reduceRight`	Fold left / right
`keys` / `values` / `entries`	Iterator of indices/values/pairs
`join(separator?)`	Join to string
`Object.groupBy(arr, fn)`	Group into object of arrays (ES2024)

💡 Examples

See parent topic notes for runnable snippets; this page is the complete method index.

⚠️ Pitfalls

Mutating methods return None in Python — do not chain sort() / reverse() expecting a new list.
Default JS sort() compares strings — pass (a,b) => a-b for numbers.
SQL function names differ by dialect — verify Postgres vs MySQL docs.
Django QuerySet.update() skips save() signals and auto auto_now fields on models.

Methods

JavaScript · Methods

Map & Set Methods

JavaScript · Methods reference

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📋 Overview 🔧 Methods Static Mutating Non-mutating (ES2023+)Search & iterate 💡 Examples ⚠️ Pitfalls 🔗 Related