To help you perform common tasks efficiently, JavaScript provides a wide variety of array methods. These methods allow you to add, remove, find, and transform array elements with ease.
1. JavaScript Array length
The length property of an array returns the number of elements in the array. It automatically updates as elements are added or removed.
let a = ["HTML", "CSS", "JS", "React"];
console.log(a.length);
The code defines an array 'a' containing the elements "HTML", "CSS", "JS", and "React".
a.length returns the number of elements in the array.
The length property returns the length (size) of an array.
2. JavaScript Array toString() Method
The toString() method converts the given value into the string with each element separated by commas.
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let myList = fruits.toString();
console.log(myList)
Output
Banana,Orange,Apple,Mango
Every JavaScript object has a toString() method.
The toString() method is used internally by JavaScript when an object needs to be displayed as a text (like in HTML), or when an object needs to be used as a string.
3. JavaScript Array at()
ES2022 introduced the array method at():
Example
Get the third element of fruits using at():
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits.at(2);
console.log(fruit);
Output
Apple
Get the third element of fruits using []:
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits[2];
Output
Apple
The at() method returns an indexed element from an array.
The at() method returns the same as [].
at() is an ECMAScript 2022 feature.
Many languages allow negative bracket indexing like [-1] to access elements from the end of an object / array / string.
This is not possible in JavaScript, because [] is used for accessing both arrays and objects. obj[-1] refers to the value of key -1, not to the last property of the object.
The at() method was introduced in ES2022 to solve this problem.
4. JavaScript Array join() Method
This join() method creates and returns a new string by concatenating all elements of an array. It uses a specified separator between each element in the resulting string.
- It behaves just like toString(), but in addition you can specify the separator.
let a = ["HTML", "CSS", "JS", "React"];
console.log(a.join('|'));
Output
HTML|CSS|JS|React
The join('|') method combines the array elements into a single string, with each element separated by a pipe (|) character.
5. Popping and Pushing
When you work with arrays, it is easy to remove elements and add new elements.
This is what popping and pushing is:
Popping items out of an array, or pushing items into an array.
JavaScript Array.pop() Method
The pop() method removes the last element from an array:
let a = [20, 30, 40, 50];
a.pop();
console.log(a);
Output
[20,30,40]
The pop() method returns the value that was "popped out".
JavaScript Array.push() Method
The push() method is used to add an element at the end of an Array. As arrays in JavaScript are mutable objects, we can easily add or remove elements from the Array.
let a = [10, 20, 30, 40, 50];
a.push(60);
a.push(70, 80, 90);
console.log(a);
Output
[10,20,30,40,50,60,70,80,90]
The push() method returns the new array length.
6. Shifting Elements
Shifting is equivalent to popping, but working on the first element instead of the last.
** JavaScript Array.shift() Method**
The shift() method removes the first array element and "shifts" all other elements to a lower index.
let a = [20, 30, 40, 50];
a.shift();
console.log(a);
Output
[30,40,50]
The shift() method returns the value that was "shifted out".
** JavaScript Array.unshift() Method**
The unshift() method adds a new element to an array (at the beginning), and "unshifts" older elements:
let a = [20, 30, 40];
a.unshift(10, 20);
console.log(a);
Output
[10,20,20,30,40]
The unshift() method returns the new array length
7. Array.isArray()
ECMAScript 5 (JavaScript 2009) added the new method Array.isArray() to JavaScript:
This method is used to check wheather the data is in Array Format or Not.
const fruits = ["Banana", "Orange", "Apple"];
console.log(Array.isArray(fruits));
Output
true
8. JavaScript Array delete()
Using delete() leaves undefined holes in the array.
Use pop() or shift() instead.
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
delete fruits[0];
console.log(fruits);
Output
[ <1 empty item>, 'Orange', 'Apple', 'Mango']
9. Merging Arrays (Concatenating)
In programming languages, concatenation means joining strings end-to-end.
Concatenation "snow" and "ball" gives "snowball".
Concatenating arrays means joining arrays end-to-end.
JavaScript Array concat() Method
The concat() method is used to concatenate two or more arrays and it gives the merged array.
let a1 = [11, 12, 13];
let a2 = [14, 15, 16];
let a3 = [17, 18, 19];
let newArr = a1.concat(a2, a3);
console.log(newArr);
Output
[11,12,13,14,15,16,17,18,19]
The concat() method does not change the existing arrays. It always returns a new array.
The concat() method can take any number of array arguments.
The concat() method can also take strings as arguments:
const arr1 = ["Emil", "Tobias", "Linus"];
const myChildren = arr1.concat("Peter");
console.log(myChildren)
Output
[ 'Emil', 'Tobias', 'Linus','Peter' ]
10. Array copyWithin()
The copyWithin() method copies array elements to another position in an array:
Examples
Copy to index 2, all elements from index 0:
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.copyWithin(2, 0);
console.log(fruits);
Output
['Banana','Orange','Banana','Orange']
Copy to index 2, the elements from index 0 to 2:
const fruits = ["Banana", "Orange", "Apple", "Mango", "Kiwi"];
fruits.copyWithin(2, 0, 2);
console.log(fruits);
Output
['Banana','Orange','Banana','Orange','Kiwi']
The copyWithin() method overwrites the existing values.
The copyWithin() method does not add items to the array.
The copyWithin() method does not change the length of the array.
11. Flattening an Array
Flattening an array is the process of reducing the dimensionality of an array.
Flattening is useful when you want to convert a multi-dimensional array into a one-dimensional array.
JavaScript Array flat()
ES2019 Introduced the Array flat() method.
The flat() method creates a new array with sub-array elements concatenated to a specified depth.
const myArr = [[1,2],[3,4],[5,6]];
const newArr = myArr.flat();
console.log(myArr) // it doesn't modify the original Array
console.log(newArr) // it return new Array as output
Output
[[1,2],[3,4],[5,6]]
[1,2,3,4,5,6]
- flat() is an ECMAScript 2019 feature.
12. JavaScript Array flatMap()
ES2019 added the Array flatMap() method to JavaScript.
The flatMap() method first maps all elements of an array and then creates a new array by flattening the array.
flatMap() is a combination of:
map() → transforms each element.
flat() → flattens one level of nested arrays
const myArr = [1, 2, 3, 4, 5, 6];
const newArr = myArr.flatMap(x => [x, x * 10]);
console.log(myArr)
console.log(newArr)
Output
[1, 2, 3, 4, 5, 6]
[
1,10,2,20,3,
30,4,40,5,50,
6,60
]
Difference Between map() and flatMap()
Using map()
const arr = [1, 2, 3];
const result = arr.map(x => [x, x * 2]);
console.log(result);
Output:
[
[1, 2],
[2, 4],
[3, 6]
]
Using flatMap()
const arr = [1, 2, 3];
const result = arr.flatMap(x => [x, x * 2]);
console.log(result);
Output:
[1, 2, 2, 4, 3, 6]
flatMap() executes a callback function on each array element and then combines (flattens) the returned arrays into a single array by removing one level of nesting.
13. Splicing and Slicing Arrays
The splice() method adds new items to an array.
The slice() method slices out a piece of an array.
JavaScript Array splice()
splice() is used to add, remove, or replace elements in an array.
- It modifies the original array.
Syntax
array.splice(start, deleteCount, item1, item2, ...)
1. Remove Elements
const fruits = ["Apple", "Banana", "Mango", "Orange"];
fruits.splice(1, 2);
console.log(fruits);
Output
["Apple", "Orange"]
What happened?
Index: 0 1 2 3
Array: ["Apple","Banana","Mango","Orange"]
Start at index 1 ("Banana")
Delete 2 elements:
"Banana", "Mango"
Remaining:
["Apple", "Orange"]
2. Add Elements
const fruits = ["Apple", "Mango"];
fruits.splice(1, 0, "Banana");
console.log(fruits);
Output
["Apple", "Banana", "Mango"]
What happened?
Start at index 1
Delete 0 elements
Insert "Banana"
3. Replace Elements
const fruits = ["Apple", "Banana", "Mango"];
fruits.splice(1, 1, "Orange");
console.log(fruits);
Output
["Apple", "Orange", "Mango"]
What happened?
Start at index 1
Remove 1 element ("Banana")
Insert "Orange"
4. Add Multiple Elements
const fruits = ["Apple", "Mango"];
fruits.splice(1, 0, "Banana", "Orange");
console.log(fruits);
Output
["Apple", "Banana", "Orange", "Mango"]
5. Return Value of splice()
splice() returns the removed elements.
const fruits = ["Apple", "Banana", "Mango"];
let removed = fruits.splice(1, 1);
console.log(removed);
console.log(fruits);
Output
["Banana"]
["Apple", "Mango"]
6. Using Negative Index
const fruits = ["Apple", "Banana", "Mango", "Orange"];
fruits.splice(-2, 1);
console.log(fruits);
Output
["Apple", "Banana", "Orange"]
Explanation
-1 → Orange
-2 → Mango
-3 → Banana
-4 → Apple
Start from "Mango" and delete 1 element.
So splice() is the CRUD method of arrays because it can:
Create (add elements)
Read (you can get removed elements)
Update (replace elements)
Delete (remove elements)
JavaScript Array toSpliced()
ES2023 added the Array toSpliced() method as a safe way to splice an array without altering the original array.
- The difference between the new toSpliced() method and the old splice() method is that the new method creates a new array, keeping the original array unchanged, while the old method altered the original array.
const months = ["Jan", "Feb", "Mar", "Apr"];
const spliced = months.toSpliced(0, 1);
console.log(months)
console.log(spliced)
Output
['Jan','Feb','Mar','Apr']
['Feb','Mar','Apr']
Here it doesn't modify the original Array so it is safe when we need our original Array in entire code.
JavaScript Array slice()
slice() is used to extract a portion of an array and create a new array.
- It does not modify the original array.
Syntax
array.slice(start, end)
start => Starting index (included)
end => Ending index (excluded)
Example 1: Basic Usage
const fruits = ["Apple", "Banana", "Mango", "Orange"];
let result = fruits.slice(1, 3);
console.log(result);
Output
["Banana", "Mango"]
Explanation:
Indexes:
0 -> Apple
1 -> Banana
2 -> Mango
3 -> Orange
slice(1,3) means:
Start from index 1
Stop before index 3
So it returns:
["Banana", "Mango"]
Example 2: Omitting end
const fruits = ["Apple", "Banana", "Mango", "Orange"];
console.log(fruits.slice(2));
Output
["Mango", "Orange"]
It starts from index 2 and takes everything till the end.
Example 3: Copy an Array
const fruits = ["Apple", "Banana", "Mango"];
const copy = fruits.slice();
console.log(copy);
Output
["Apple", "Banana", "Mango"]
This is a common way to create a shallow copy of an array.
Example 4: Negative Index
const fruits = ["Apple", "Banana", "Mango", "Orange"];
console.log(fruits.slice(-2));
Output
["Mango", "Orange"]
Negative indexes count from the end:
-1 -> Orange
-2 -> Mango
-3 -> Banana
-4 -> Apple
Example 5: Original Array Remains Unchanged
const fruits = ["Apple", "Banana", "Mango"];
let result = fruits.slice(1);
console.log(result);
console.log(fruits);
Output
["Banana", "Mango"]
["Apple", "Banana", "Mango"]
Notice that fruits is unchanged.
slice() is used to extract a part of an array and return it as a new array without changing the original array.
References
https://www.w3schools.com/js/js_array_methods.asp
https://www.geeksforgeeks.org/javascript/javascript-array-methods/
https://www.programiz.com/javascript/library/array
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