What is an Array?

Array is an collection of elements of same datatype. But in JS Array is an collection of elements of multiple datatypes.
in JS, Array is an Object. You can suppose index of an Array element as it's key and element itself as it's value, just like Object's key value pair.
Array is a non primitive Datatype.
First element is at 0th index.
Array in JS, also support negative indexing.

Ways of declaring array in JavaScript.

Using Array Constructor.

if you pass a number as an arguments to the constructor, it will create empty array of that size.
But if you pass a string or more than one parameter it will treat them as the elements.

const arr1 = new Array(4);
console.log(arr1.length); // Output -> 4 
console.log(arr1[0]);     // Output -> undefined

const arr2 = new Array(4,5);
console.log(arr2.length); // Output -> 2
console.log(arr2[0]);     // Output -> 4

const arr3 = new Array('Kartik');
console.log(arr3.length); // Output -> 1
console.log(arr3[0]);     // Output -> Kartik

Using `Array.of()` method

Create an Array using Array.of() method of the Array class.

const arr = Array.of(20, 'Kartik', 3.14, false);
console.log(arr) // Output -> [ 20, 'Kartik', 3.14, false]

Using `[]`

Easiest way to create an Array is using [] square brackets

const arr = [10, 'Hitesh', 3.98, true];
console.log(arr) // Output -> [10, 'Hitesh', 3.98, true]

Ways to access array elements

Using `[]` square bracket notations.

const arr = [10, 'Hitesh', 3.98, true];
console.log(arr[0]);
console.log(arr[1]);
console.log(arr[2]);
console.log(arr[3]);
// Output ->
// 10
// Hitesh
// 3.98
// true

Using `at()` method

const arr = [10, 'Hitesh', 3.98, true];
console.log(arr.at(0));
console.log(arr.at(1));
console.log(arr.at(2));
console.log(arr.at(3));
// Output ->
// 10
// Hitesh
// 3.98
// true

All Array Methods!!

1. at()

Syntax - at(index)
Using at() method you can fetch the element at a particular index by passing index number as a parameter.
It returns undefined if the element is not present at that specific index.

const arr = ['React', 'Angular', 'ExpressJS', 'MongoDB', 'Nodejs', 'NextJs'];
console.log(arr.at(1)); // Output -> Angular
console.log(arr.at(6)); // Output -> undefined

2. concat()

Syntax - concat(value0, value1, ....., valueN)
It accepts n number of arrays as parameter(s).
We can combine multiple arrays using concat() method.
It doesn't modify original array instead returns new array.
If we don't provide any parameter to the method, it creates a shallow copy of the array.
In the below example, we are combining 3 arrays.

const languages = ['JavaScript', 'Go'];
const styling = ['CSS', 'Tailwind'];
const frameworks = ['React', 'Angular'];
const concatedArray = languages.concat(styling, frameworks);

console.log('concatedArray ->' ,concatedArray); 
// Output -> [ 'JavaScript', 'Go', 'CSS', 'Tailwind', 'React', 'Angular' ]

3. copyWithin()

Syntax copyWithin(target, start, end).
It accepts three parameters.
- target (Optional) - the target index to where elements will be copied. Default is 0.
- start (Optional) - the start index from where the elements will be copied. Default is 0.
- end (Optional) - the end index till where elements will be copied. Default is 0
It copies the elements from the array to a different location of the same array.
It modifies the existing array but not the length of the array.
Here, in below example we have to copy from start index 3 and end index 6(not inclusive) so the elements that we are copying are C++, Java, Go and will replace the elements starting from the targeted index 1 that are python, C, C++.

const languages = ['JavaScript', 'Python', 'C', 'C++', 'Java', 'Go', 'Swift'];
languages.copyWithin(1, 3, 6);

console.log('languages -> ',languages);
// Output -> ['Javascript', 'C++', 'Java', 'Go', 'Java', 'Go', 'Swift', 'Ruby']

4. entries()

Syntax - entries();
entries() method creates a new Array Iterator Object.
It doesn't modifies the current array.
It returns a new Array Iterator Object
The output of this method is Array of multiple Arrays with each consist of 2 values i.e. one index and one element itself. You can see in the example below.

const languages = ['Javascript', 'Python', 'Go', 'Swift', 'Ruby'];
const iterator = languages.entries();
for(const element of iterator) {
    console.log(element);
}
// Output ->
// [ 0, 'Javascript' ] 
// [ 1, 'Python' ]
// [ 2, 'Go' ]
// [ 3, 'Swift' ]
// [ 4 'Ruby' ]

5. every()

Syntax - every((element, index, array) => { /* … */ } )
every() accepts a arrow function as a parameter
- arrow function - It executes for each element of the array. It also accepts 3 parameter
  - element - element of that particular iteration
  - index - index of the element.
  - array - the array itself.
It returns true when a specific condition is true for all the elements in the array else returns false.
Below example explains how every method on first array returns true as all the elements satisfies the condition of type string whereas the second array returns false.

const languages = ['Javascript', 'Python', 'C', 'C++', 'Java', 'Go'];
let isStringArray = languages.every((element) => {
    return typeof element == 'string' ? true : false
});
console.log(isStringArray); // Output -> true

const randomArray = ['this', 'is', 'a', 'random', 'array', 100];
isStringArray = randomArray.every((element) => {
    return typeof element == 'string' ? true : false
});
console.log(isStringArray); // Output -> false

6. fill()

Syntax - fill(value, start, end)
It accepts three parameter
- value - value that we have to fill from start to end Index.
- start (Optional) - starting index from where value will be filled in the array. Default is 0.
- end (Optional) - end index till where value will be filled in the array. end index is not inclusive in the range. Default is array.length.
Replaces the elements of the array by the value depending on the start and end index we provide to the method.
Default start value is 0 and end value is array.length.
It returns the modified array that is filled with value.
In the Below Example, value is Java, Start is 1 and end is 3. So the element on index 1,2 are replaced or we can say filled by the value.

const languages = ['Javascript', 'Python', 'Go', 'Swift', 'Ruby'];
languages.fill('Java', 1, 3);

console.log(languages);
// Output -> [ 'Javascript', 'Java', 'Java', 'Swift', 'Ruby' ]

7. filter()

Syntax - filter((element, index, array) => { /* … */ } )
filter() accepts a arrow function as a parameter
- arrow function - It executes for each element of the array. It also accepts 3 parameter
  - element - element of that particular iteration
  - index - index of the element.
  - array - the array itself.
It filters the elements based on a the condition from the array and, creates and returns a shallow copy of elements of an array that passes the condition provided inside arrow function.
It doesn't modify the original array.
In the below example we are filtering the elements which are greater than or equal to 100.

const numbers = [10, 100, 45, 3000, 225, 2];
const numbersgt100 = numbers.filter((element) => {
    return element >= 100 ? true : false
});

console.log(numbersgt100); // Output -> [ 100, 3000, 225 ]

8. find()

Syntax find((element, index, array) => { /* … */ } ).
find() accepts a arrow function as a parameter
- arrow function - It executes for each element of the array. It also accepts 3 parameter
  - element - element of that particular iteration
  - index - index of the element.
  - array - the array itself.
It finds and returns the first element from array which satisfies the condition inside the arrow.
In below example, we find the first element that starts with 'H' and i.e. Hitesh.

const names = ['Kartik', 'Hitesh', 'Harsh', 'Anirudh'];
const result = names.find((element) => {
    return element.startsWith('H') ? true : false
});

console.log(result); // Output -> Hitesh

9. findIndex()

Syntax findIndex((element, index, array) => { /* … */ } ).
findIndex() accepts a arrow function as a parameter
- arrow function - It executes for each element of the array. It also accepts 3 parameter
  - element - element of that particular iteration
  - index - index of the element.
  - array - the array itself.
It finds and returns the index of first element from array which satisfies the arrow condition.
It's just like find() method but instead of element it returns the index of the element.
In below example, we find the first element that starts with 'H' i.e Hitesh and it's index is 1.

const names = ['Kartik', 'Hitesh', 'Harsh', 'Anirudh'];
const result = names.findIndex((element) => {
    return element.startsWith('H') ? true : false
});

console.log(result); // Output -> 1

10. findLast()

Syntax findLast((element, index, array) => { /* … */ } ).
findLast() accepts a arrow function as a parameter
- arrow function - It executes for each element of the array. It also accepts 3 parameter
  - element - element of that particular iteration
  - index - index of the element.
  - array - the array itself.
It finds and returns the last element from array which satisfies the arrow condition.
It is opposite of find() method as find() method returns the first element.
While writing this article, node.js doesn't support this method. Maybe in future it might come.
In below example, we find the last element that starts with 'H'.

const names = ['Kartik', 'Hitesh', 'Harsh', 'Anirudh'];
const result = names.findLast((element) => {
    return element.startsWith('H') ? true : false
});

console.log(result);// Output -> Harsh

11. findLastIndex()

Syntax findLadtIndex((element, index, array) => { /* … */ } ).
findLastIndex() accepts a arrow function as a parameter
- arrow function - It executes for each element of the array. It also accepts 3 parameter
  - element - element of that particular iteration
  - index - index of the element.
  - array - the array itself.
It finds and returns the index of last element from array which satisfies the arrow condition.
It's just like findLast() method but instead of element it returns the index of the element.
It is opposite of findIndex() method as findIndex() method returns the index of first element.
In below example, we find the last element that starts with 'H' i.e Harsh and it's index is 2.

const names = ['Kartik', 'Hitesh', 'Harsh', 'Anirudh'];
const result = names.findLastIndex((element) => {
    return element.startsWith('H') ? true : false
});

console.log(result); // Output -> 2

12. flat()

Syntax - flat(depth)
flat() accepts one parameter.
- depth (Optional) - the level of flattening of array. Default depth value is 1.
flat() method flattens the nested arrays in an array depending upon the depth we specify. If we want to flatten the nested arrays at maximum level possible than we can provide Infinity as a depth parameter.
It does not modifies the existing array instead returns the new flattened array.
In the below example we are first flattening the array at the depth of 1 and in the second result we are flattening at the maximum level i.e. Infinity possible so it flattens all the elements.

const names = [['Kartik'], [['Hitesh', 'Harsh']] , [[['Anirudh', 'Akash']]] ];
const result1 = names.flat(1);
console.log(result1);
// Output -> [ 'Kartik', [ 'Hitesh', 'Harsh' ], [ [ 'Anirudh', 'Akash' ] ] ]

const result2 = names.flat(Infinity);
console.log(result2);
// Output -> [ 'Kartik', 'Hitesh', 'Harsh', 'Anirudh', 'Akash' ]

13. flatMap()

Syntax flatMap((element, index, array) => { /* … */ } ).
flatMap() accepts a arrow function as a parameter
- arrow function - It executes for each element of the array. It also accepts 3 parameter
  - element - element of that particular iteration
  - index - index of the element.
  - array - the array itself.
flatMap() method is a combination of map() and flat() method.
It does not modifies the existing array instead returns the new flattened and mapped array.
First it map the elements and then flattens the resulted map by the depth of 1.
In below example we are comparing the result of map() and flatmap() method. You can see the result of map() method contains nested arrays when we apply split method to each element of the array, but the result of the flatMap() is a flattened array.

const names = ['Kartik Gupta', 'Hitesh Chaudhary', 'Anurag Tiwari'];
const mapResult = names.map(e => e.split(' '));
console.log(mapResult);
// Output -> [[ 'Kartik', 'Gupta' ], [ 'Hitesh', 'Chaudhary' ], [ 'Anurag', 'Tiwari' ]]

const flatMapResult = names.flatMap(e => e.split(' '));
console.log(flatMapResult);
// Output -> [ 'Kartik', 'Gupta', 'Hitesh', 'Chaudhary', 'Anurag', 'Tiwari' ]

14. forEach()

Syntax forEach((element, index, array) => { /* … */ } ).
forEach() accepts a arrow function as a parameter
- arrow function - It executes for each element of the array. It also accepts 3 parameter
  - element - element of that particular iteration
  - index - index of the element.
  - array - the array itself.
forEach() works just like for loop but it is a method not a loop. It executes the specified function for all the elements of the array.
It neither modifies the existing array nor creates a new array.
In below example, we iterated over a numbers array using forEach() and then pushes square of each element of numbers array to the squareNumbers array.

const numbers = [1,2,3,4,5,6];
const squareNumbers = [];
numbers.forEach((element)=>{
    squareNumbers.push(element**2)
});
console.log(squareNumbers); // Output -> [ 1, 4, 9, 16, 25, 36 ]

15. Array.from()

Syntax - Array.from(arrayLike, (element, index) => { /* … */ } )
Array.from() accepts a two parameter
- arrayLike - instance of arraylike iterable and a arrow function
  - arrow function - It executes for each element of the array. It also accepts 3 parameter
    - element - element of that particular iteration
    - index - index of the element.
    - array - the array itself.
Array.from() is a static method of Array class.
Array.from creates a array from a iterable or array-like object like and will also perform the arrow function for each element of the iterable.
In the below example, I have passed 'Kartik' (String) as a array-like iterable and for every character it performs toUpperCase() to capitalize each character and stored it in an array as separate element.

const myName = Array.from('Kartik', (element => {
    return element.toUpperCase();
}));

console.log(myName); // Output -> [ 'K', 'A', 'R', 'T', 'I', 'K' ]

16. includes()

Syntax includes(searchElement, fromIndex)
includes() method accepts two parameters.
- searchElement - Element which we want to check whether it is included in the array or not -fromIndex (Optional) - starting index from where we want to check the searchElement. Default is 0
includes() method returns true if the element is included in the array else it returns false.
In the below example, we are checking whether the array includes the name 'Hitesh' or not.

const names = ['Kartik', 'Hitesh', 'Anurag', 'Anirudh', 'Akash'];

console.log(names.includes('Hitesh')); // Output -> true

console.log(names.includes('Hitesh', 2)); // Output -> false

17. indexOf()

Syntax indexOf(searchElement, fromIndex)
indexOf() method accepts two parameters.
- searchElement - Element which we want to check in the array
- fromIndex (Optional) - starting index from where we want to check the searchElement. Default is 0
indexOf() method returns the first index of the searchElement if the element is present in the array else it returns -1.
In the below example we are checking what is first the index of 'Hitesh'.

const names = ['Kartik', 'Hitesh', 'Anurag', 'Anirudh', 'Akash'];
console.log(names.indexOf('Hitesh')); // Output -> 1

console.log(names.indexOf('Hitesh', 2)); // Output -> -1

18. Array.isArray()

Syntax Array.isArray(value)
Array.isArray() takes value as a parameter and check whether the value is an array or not.
Array.isArray() is a static method of Array class.
Array.isArray() returns true if the value is an array else it returns false.
In below example, we are checking if the provided value is an Array or not.

const anArray = [1,2,3,4];
console.log(Array.isArray(anArray)); // Output -> true

const notAnArray = 1234;
console.log(Array.isArray(notAnArray)); // Output -> false

19. join()

Syntax join(separator)
join() accepts one parameter
- separator - used for separating array elements after joining in a string.
join() methods joins all the elements of the array and creates a string in which elements are separated using the separator parameter.
In the below Example, we are joining all the elements of the array as String separated by ,

const webStack = ['Javascript', 'HTML', 'CSS'];
console.log(webStack.join(', ')); // Output-> Javascript, HTML, CSS

20. keys()

Syntax keys()
keys() method returns a new Array Iterator object that contains the keys for each index in the array.
keys() method is mostly used with objects and in JS Array is also an object, so Array inherit the keys() method from its parent class and that is Object.
Refer below example.

const anArray = ['Kartik', 'Hitesh', 'Anurag', 'Anirudh'];
const keys = anArray.keys();
for(let key of keys) {
    console.log(key);
}

// Output -> 
// 0
// 1
// 2
// 3

21. lastIndexOf()

Syntax lastIndexOf(searchElement, fromIndex)
lastIndexOf() method accepts two parameters.
- searchElement - Element which we want to check in the array
- fromIndex (Optional) - starting index from where we want to check the searchElement. Default is 0
lastIndexOf() method returns the last index of the searchElement if the element is present in the array else it returns -1.
lastIndexOf() method doesn't ignore the elements at indexes before fromIndex. It just wrap around and iterate from 0 to fromIndex-1 after reaching the end of the array.
In the below example we are checking what is the last index of 'Kartik'.

const names = ['Kartik', 'Hitesh', 'Kartik', 'Anirudh', 'Akash'];
console.log(names.lastIndexOf('Kartik')); // Output -> 2

console.log(names.lastIndexOf('Kartik', 1)); // Output -> 0

22. map()

Syntax map((element, index, array) => { /* … */ })
map() accepts a arrow function as a parameter
- arrow function - It executes for each element of the array. It also accepts 3 parameter
  - element - element of that particular iteration
  - index - index of the element.
  - array - the array itself.
map() method creates a new array which is populated based on the condition applied on the each element of the array.
It doesn't modifies the original array but instead return a new array.
In below example we are appending the index of the element to the element itself using map().

const names = ['Kartik', 'Hitesh', 'Anurag', 'Hitesh', 'Akash'];
const newNames = names.map((element, index) => {
    return element +' ' + index;
});
console.log(newNames); 
// Output -> [ 'Kartik 0', 'Hitesh 1', 'Anurag 2', 'Hitesh 3', 'Akash 4' ]

23. Array.of()

Syntax Array.of(element0, element1, /* … ,*/ elementN)
Array.from() is a static method of Array class.
It accepts n numbers of elements and creates a array out of it.
In the below example we have passed 3 arguments/parameter to the method and as a result we got a array of length 3.

const anArray = Array.of('JavaScript', 'HTML', 'CSS');
console.log(anArray); // Output -> ['JavaScript', 'HTML', 'CSS']

24. pop()

Syntax pop()
pop() method removes the last element from the array.
It returns that element that is poped out or removed from the end.
It modifies the original array.
In below example we are applying pop() to the numbers array.

const numbers = [9, 20, 34, 53, 71, 29, 45];
console.log(numbers.pop());
// Output -> 45
console.log(numbers.length);
// Output -> 6
console.log(numbers);
// Output -> [9, 20, 34, 53, 71, 29]

25. push()

Syntax push(element0, element1, /* … ,*/ elementN)
It adds n numbers of elements provided in parameters at the end of the array
It returns the length of the array.
It modifies the original array.

const numbers = [9, 20, 34, 53, 71, 29, 45];

console.log(numbers.push(50));
// Output -> 8
console.log(numbers);
// Output -> [9, 20, 34, 53, 71, 29, 45, 50]

console.log(numbers.push(29, 68)); 
// Output -> 10
console.log(numbers);
// Output -> [9, 20, 34, 53, 71, 29, 45, 50, 29, 68]

26. reduce()

Syntax reduce((previousValue, currentValue, currentIndex, array) => { /* … */ }, initialValue)
reduce() method accepts a arrow function and a initialValue as a parameter
- arrow function can accept 4 parameters.
  - previousValue - the result of the previous operation
  - currentValue - current element of the array
  - currentIndex - index of the element
  - array - the array itself
- initialValue (Optional) - value of previousValue parameter in the callback for the first iteration.
For the first iteration, -If initialValue is specified than previoudValue is equal to the initialValue and currentValue is equal to the first element of the array.
- If initialValue is not specified than previoudValue is equal to the first element and first element is skipped from the iteration of the array and currentValue is equal to the second element of the array.
reduce() method executes arrow function on every element of the array and results into a single value.
In below example, we are applying reduce method on the array to generate a reduced string.

const factArr = ['Honesty', 'is', 'the', 'best', 'policy'];
const universalTruth = factArr.reduce((pv, cv) => {
    return pv + ' ' + cv;
},'');

console.log(universalTruth);
// Output -> Honesty is the best policy

27. reduceRight()

Syntax reduceRight((accumulator, currentValue, index, array) => { /* … */ }, initialValue)
reduceRight() is same as reduce(). The only difference is the direction of iteration. reduce() iterate from left to right whereas reduceRight() iterates from right to left. Please refer to reduce() method first before understanding reduceRight().
reduceRight() method accepts a arrow function and a initialValue as a parameter
- arrow function can accept 4 parameters.
  - accumulator - the result of the previous operation
  - currentValue - current element of the array
  - currentIndex - index of the element
  - array - the array itself
- initialValue (Optional) - value of accumulator parameter in the callback for the first iteration.
For the first iteration, -If initialValue is specified than accumulator is equal to the initialValue and currentValue is equal to the last element of the array.
- If initialValue is not specified than accumulator is equal to the last element and last element is skipped from the iteration of the array and currentValue is equal to the last second element of the array.
reduceRight() method executes arrow function on every element of the array and results into a single value.
In below example, we are applying reduce method on the array to generate a reduced string.

const factArr = ['Honesty', 'is', 'the', 'best', 'policy'];
const universalTruth = factArr.reduce((pv, cv) => {
    return pv + ' ' + cv;
},'');

console.log(universalTruth);
// Output -> ploicy best the is Honesty.

28. reverse()

Syntax reverse()
reverse() method reverses the array.
It modifies the original array and returns the reversed array.
check the below example.

const names = ['Kartik', 'Hitesh', 'Anurag', 'Anirudh', 'Akash'];
console.log(names.reverse())
// Output -> ['Akash', 'Anirudh', 'Anurag', 'Hitesh', 'Kartik']

29. shift()

Syntax shift()
shift() method removes the first element from the array.
It returns the element that is removed.
It modifies the original array.
In below example we are applying shift() to the numbers array.

const numbers = [9, 20, 34, 53, 71, 29, 45];
console.log(numbers.shift());
// Output -> 9
console.log(numbers.length);
// Output -> 6
console.log(numbers);
// Output -> [ 20, 34, 53, 71, 29, 45 ]

30. slice()

Syntax slice(start, end)
slice() accepts two parameters.
- start (Optional) - Start Index. Default is 0.
- end (Optional) - End Index (not inclusive). Default is array.length.
It doesn't modifies the original array.
It slices out a specific portion of array based on start and end Index values.
It returns the sliced array.
Refer to below example.

const names = ['Kartik', 'Hitesh', 'Anurag', 'Anirudh', 'Akash'];
console.log(names.slice(1,3));
// Output -> ['Hitesh', 'Anurag']

31. some()

Syntax some((element, index, array) => { /* … */ } )
some() accepts a arrow function as a parameter
- arrow function - It executes for each element of the array. It also accepts 3 parameter
  - element - element of that particular iteration
  - index - index of the element.
  - array - the array itself.
It returns true when a specific condition is satsifies for at least one element in the array else returns false.
Below example explains even if one element satisfies the condition then the result is true.

const randomArray = ['this', 'is', 'a', 'random', 'array', 100];
let isNumberArray = randomArray.some((element) => {
    return typeof element == 'number' ? true : false
});
console.log(isNumberArray); // Output -> true

const languages = ['Javascript', 'Python', 'C', 'C++', 'Java', 'Go'];
isNumberArray = languages.some((element) => {
    return typeof element == 'number' ? true : false
});
console.log(isNumberArray); // Output -> false

32. sort()

Syntax sort((a, b) => { /* … */ } )
It accepts a arrow function
- arrow function (Optional) - It executes logic of comparisions of two elements. It also accepts 2 parameter.
  - a - First element for comparision.
  - b - Second element for comparision.
sort() is used to sort the array based on the comparision arrow function.
If arrow function is not specified than it will sort based the elements based on the string comparision.
if the sorting arrow function returns value less than 0 than a will come before b and vice versa.
If the sorting arrow function return 0, it will keep the a and b at original place.
In below example we are sorting elements in decending order.

const numbers = [9, 20, 34, 53, 71, 29, 45];
numbers.sort((a,b) => {
    return a > b ? -1 : 1;
});
console.log(numbers);
// Output -> [71, 53, 45, 34, 29, 20, 9]

33. splice()

Syntax splice(start, deleteCount, item1, item2, ... itemN)
splice() accepts multiple paramters.
- start - index at which to start changing the array.
- deleteCount - How many elements to delete from start
- item1, item2, ... itemN - number of items to replace with the deleted elements.
It deletes the elements from start index to start + deleteCount Index and will replace with the n items passed to the method.
It returns the array of deleted elements.
It also changes the length of the array.
It modifies the original array by replacing the deleted elements by the other passed items.
If deletedCount is 0 then no elements would be deleted and items will be added to the start index pushing the later elements forward in the array resulting in increasing the length of the array.
If no items are passed to the method than the elements will be deleted from start index to start + deletedCount index resulting in decreasing the length of the array.
In the below example, we deleting replacing "Anurag", "Anirudh" and replacing them by "Ajinkya", "Mandeep", "Shubham".

const names = ['Kartik', 'Hitesh', 'Anurag', 'Anirudh', 'Akash'];
console.log(names.splice(2, 2, "Ajinkya", "Mandeep", "Shubham"));
// Output -> [ 'Anurag', 'Anirudh' ]

console.log(names);
// Output ->  ['Kartik', 'Hitesh', 'Ajinkya', 'Mandeep', 'Shubham', 'Akash']

34. toLocaleString()

Syntax toLocaleString(locales, options);
toLocalString() accepts two parameters.
- locales - specific language format to use
- options - object to set properties like timezone
It is mostly used with Date and Time, Numbers or Objects sometimes. Very rarely used with Arrays.
The toLocaleString() method returns a string representing the elements of the array.
The elements are converted to Strings using their toLocaleString methods and these Strings are separated by a locale-specific String (such as a comma ",").

const array1 = [1, 'a', new Date('28 Aug 2022 18:35:00 UTC')];
const localeString = array1.toLocaleString('hi-IN', { timeZone: 'IST' });
console.log(localeString);
// Output -> 1,a,29/8/2022, 12:05:00 am

35. toString()

Syntax toString()
It joins all the elements of arrays seperated by commas(-).
It returns the string of elements seperated by commas and it doesn't modifies the original array.
Refer below example.

const numbers = [9, 20, 34, 53, 71, 29, 45];
console.log(numbers.toString());
// Output -> 9,20,34,53,71,29,45

console.log(numbers);
// Output -> [9, 20, 34, 53, 71, 29, 45]

36. unshift()

Syntax unshift(element0, element1, /* … ,*/ elementN)
It adds n numbers of elements provided in parameter to the start of the array.
It returns the length of the array.
It modifies the original array.

const numbers = [9, 20, 34, 53, 71, 29, 45];

console.log(numbers.unshift(50));
// Output -> 8
console.log(numbers);
// Output -> [50,  9, 20, 34, 53, 71, 29, 45]

console.log(numbers.unshift(29, 68)); 
// Output -> 10
console.log(numbers);
// Output -> [29, 68, 50,  9, 20, 34, 53, 71, 29, 45]

37. values()

Syntax values()
values() method returns a new array iterator object that contains the values for each index in the array.
values() method is mostly used with objects and in JS Array is also an object, so Array inherit the values() method from its parent class and that is Object.
Refer Below Example

const anArray = ['Kartik', 'Hitesh', 'Anurag', 'Anirudh'];
const values = anArray.values();
for(let value of values) {
    console.log(value);
}

// Output -> 
// 'Kartik'
// 'Hitesh'
// 'Anurag'
// 'Anirudh'

JavaScript (JS) -Array and Methods!

Table of contents

What is an Array?

Ways of declaring array in JavaScript.

Using Array Constructor.

Using Array.of() method

Using []

Ways to access array elements

Using [] square bracket notations.

Using at() method

All Array Methods!!

1. at()

2. concat()

3. copyWithin()

4. entries()

5. every()

6. fill()

7. filter()

8. find()

9. findIndex()

10. findLast()

11. findLastIndex()

12. flat()

13. flatMap()

14. forEach()

15. Array.from()

16. includes()

17. indexOf()

18. Array.isArray()

19. join()

20. keys()

21. lastIndexOf()

22. map()

23. Array.of()

24. pop()

25. push()

26. reduce()

27. reduceRight()

28. reverse()

29. shift()

30. slice()

31. some()

32. sort()

33. splice()

34. toLocaleString()

35. toString()

36. unshift()

37. values()

Using `Array.of()` method

Using `[]`

Using `[]` square bracket notations.

Using `at()` method