JavaScript Array Methods
JavaScript Array length
The length property returns the length (size) of an array:
The length property can also be used to set the length of an array:
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.length = 2;
JavaScript Array toString()
The toString() method returns the elements of an array as a comma separated string.
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let myList = fruits.toString();
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.
JavaScript Array at()
ES2022 introduced the array method at()
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits.at(2);
(or)
let fruit = fruits[2];
The at() method returns an indexed element from an array.
The at() method returns the same as []
at() is an ECMAScript 2022 feature.
JavaScript 2022 is supported in all modern browsers since March 2022
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.
JavaScript Array join()
The join() method also joins all array elements into a string.
It behaves just like toString(), but in addition you can specify the separator:
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()
The pop() method removes the last element from an array:
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.pop();
The pop() method returns the value that was "popped out":
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits.pop();
JavaScript Array push()
The push() method adds a new element to an array (at the end):
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.push("Kiwi");
The push() method returns the new array length:
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let length = fruits.push("Kiwi");
Shifting Elements
Shifting is equivalent to popping, but working on the first element instead of the last.
JavaScript Array shift()
The shift() method removes the first array element and "shifts" all other elements to a lower index.
The shift() method returns the value that was "shifted out".
JavaScript Array unshift()
The unshift() method adds a new element to an array (at the beginning), and "unshifts" older elements:
The unshift() method returns the new array length:
Changing Elements
Array elements are accessed using their index number
Array indexes start with 0:
[0] is the first array element
[1] is the second
[2] is the third ..
JavaScript Array length
The length property provides an easy way to append a new element to an array:
Array.isArray()
ECMAScript 5 (JavaScript 2009) added the new method Array.isArray() to JavaScript:
Array.isArray(fruits);
JavaScript Array delete()
Warning !
Using delete() leaves undefined holes in the array.
Use pop() or shift() instead.
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()
The concat() method creates a new array by merging (concatenating) existing arrays:
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:
Array copyWithin()
The copyWithin() method copies array elements to another position in an array:
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
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.
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()
The splice() method can be used to add new items to an array:
The first parameter (2) defines the position where new elements should be added (spliced in).
The second parameter (0) defines how many elements should be removed.
The rest of the parameters ("Lemon" , "Kiwi") define the new elements to be added.
The splice() method returns an array with the deleted items:
Using splice() to Remove Elements
With clever parameter setting, you can use splice() to remove elements without leaving "holes" in the array:
The first parameter (0) defines the position where new elements should be added (spliced in).
The second parameter (1) defines how many elements should be removed.
The rest of the parameters are omitted. No new elements will be added.
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
JavaScript Array slice()
The slice() method slices out a piece of an array into a new array:
The slice() method can take two arguments like slice(1, 3).
The method then selects elements from the start argument, and up to (but not including) the end argument
const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(1, 3);
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