Javascript Array Methods: Full Guide With Clear Examples

Javascript arrays come with a large amount of built-in methods. It’s impossible (and unnecessary) to memorize all of them. A better approach is to learn about them gradually: understand what each method does, when it’s useful and try it out in real code.

Over time, as you experiment and build real projects, you’ll naturally start remembering the ones you use most and your code will be cleaner, safer and even easier to maintain.

This guide organizes almost every array method with clear examples into easy-to-read tables. Consider it your roadmap for learning arrays step by step.

If you’re just starting out, this quick intro is a great place to begin: 6 Must-Know JavaScript Array Methods (With Simple Examples)

1. Transform Methods

Function	Mutates?	What It Does	Example	Output	Notes
map()	No	Transform each item; returns the same-length new array.	[1,2,3].map(n => n * 2)	[2,4,6]	Use for one-to-one transformations; avoid side-effects (forEach instead).
flatMap()	No	map() followed by one-level flattening.	[1,2].flatMap(n => [n, n * 2])	[1,2,2,4]	Useful for mapping + expanding values.
flat()	No	Flattens nested arrays by a given depth.	[1,[2,[3]]].flat(2)	[1,2,3]	Deep flattening can be expensive.

2. Filtering & Searching

Function	Mutates?	What It Does	Example	Output	Notes
filter()	No	Returns items matching a condition.	[1,2,3,4].filter(n => n % 2 === 0)	[2,4]	Creates a new, shorter array.
find()	No	Returns the first matching item.	[3,6,9].find(n => n > 4)	6	Stops as soon as it finds a match.
findIndex()	No	Returns index of the first match.	[3,6,9].findIndex(n => n > 4)	1	-
findLast()	No	Returns the last matching item.	[1,2,3,4].findLast(n => n < 4)	3	Searches from the end.
findLastIndex()	No	Index of the last match.	[1,2,3,4].findLastIndex(n => n < 4)	2	-
includes()	No	Checks if a value exists.	['a','b'].includes('a')	true	More readable than indexOf().

3. Reducing & Aggregation

Function	Mutates?	What It Does	Example	Output	Notes
reduce()	No	Combine items left → right into one output.	[1,2,3].reduce((a,n) => a + n, 0)	6	Works for sums, grouping, flattening, etc.
reduceRight()	No	Like reduce() but right → left.	['a','b','c'].reduceRight((a,c) => a + c)	'cba'	Useful for right-associative operations.

4. Condition Checking

Function	Mutates?	What It Does	Example	Output	Notes
some()	No	Returns true if any value matches.	[1,3,5].some(n => n % 2 === 0)	false	Stops early for efficiency.
every()	No	True only if all values match.	[2,4,6].every(n => n % 2 === 0)	true	Useful for validation checks.

5. Sorting & Reordering

Function	Mutates?	What It Does	Example	Output	Notes
sort()	Yes	Sort array in place.	[3,1,2].sort()	[1,2,3]	Mutates — be careful with shared state.
reverse()	Yes	Reverse array in place.	[1,2,3].reverse()	[3,2,1]	Mutates.
toSorted()	No	Returns a sorted copy.	[3,1,2].toSorted()	[1,2,3]	Safe alternative to sort().
toReversed()	No	Returns a reversed copy.	[1,2,3].toReversed()	[3,2,1]	Safe alternative to reverse().

6. Adding & Removing Items (Mutating)

Function	Mutates?	What It Does	Example	Output	Notes
push()	Yes	Add item(s) to the end.	arr.push(4)	4	Returns new length.
pop()	Yes	Remove item from the end.	arr.pop()	4	Returns removed item.
shift()	Yes	Remove first item.	arr.shift()	1	Slower than pop().
unshift()	Yes	Add item(s) to the start.	arr.unshift(0)	4	Returns new length.
splice()	Yes	Add/remove at any index.	arr.splice(1,1)	[2]	Extremely flexible but mutates.

7. Non-Mutating Alternatives

Function	Mutates?	What It Does	Example	Output	Notes
slice()	No	Extract a portion.	[1,2,3].slice(1)	[2,3]	Commonly used to copy arrays.
concat()	No	Merge arrays.	[1].concat([2,3])	[1,2,3]	Can replace push() for immutable code.
toSpliced()	No	Non-mutating version of splice().	[1,2,3].toSpliced(1,1)	[1,3]	Ideal for React/immutable patterns.

8. Combining & Converting

Function	Mutates?	What It Does	Example	Output	Notes
join()	No	Turn array into string.	['a','b'].join('-')	'a-b'	Good for CSV, lists, paths.
Array.from()	No	Convert iterable → array.	Array.from('hi')	['h','i']	Works with NodeLists, Sets, etc.
Array.of()	No	Create an array from arguments.	Array.of(1,2)	[1,2]	Avoids quirks of new Array().
Array.isArray()	No	Check if value is an array.	Array.isArray([])	true	-
indexOf()	No	First index of a value.	['a','b','a'].indexOf('a')	0	Use includes() when checking existence.
lastIndexOf()	No	Last index of a value.	['a','b','a'].lastIndexOf('a')	2	-
at()	No	Access by index (supports negatives).	[1,2,3].at(-1)	3	Cleaner than arr[arr.length - 1].

Final Summary

A compact overview with recommended use-cases.

Category	Methods	Recommended Use
Transform	map, flat, flatMap, reduce, reduceRight	Converting data, mapping, flattening, building new results.
Filter/Search	filter, find, findIndex, findLast, findLastIndex, some, every, includes	Extracting items, locating values, validation checks.
Reorder	sort, reverse, toSorted, toReversed	Sorting or reversing data; prefer non-mutating versions.
Add/Remove	push, pop, shift, unshift, splice, slice, toSpliced, concat	Managing list changes; choose non-mutating alternatives.
Utility	flat, join, Array.from, Array.of, Array.isArray, indexOf, lastIndexOf, at	Formatting, conversions, type checking, index lookups.

Final Thoughts

A few friendly tips to keep in mind as you explore javascript arrays:

• Don’t stress about memorization, focus on understanding what each method does and practicing it in small projects.
• Use mutating methods when you intentionally want to change the original array.
• Use non-mutating methods to write safer, predictable code.

Remember, it’s not about knowing every method; it’s about knowing the right one for the job and using them effectively. Take it step by step, and your array skills will grow naturally.

Happy learning and thank you for reading!