An array is a special variable in all the languages that is used to store different elements. JavaScript array contains some built-in properties that every JavaScript developer should know how to use them and when or where to use them. We can use them to add, remove, iterate, or manipulate data as per our requirements. There are some basic JavaScript array methods that every developer should know.
1. some() Method: This method checks whether at least one of the elements of the array satisfies the condition checked by the argument function.
- Example:
<script>
// JavaScript to illustrate
// lastIndexOf() method
function
isGreaterThan5(element, index, array) {
return
element > 5;
}
function
func() {
// Original array
var
array = [2, 5, 8, 1, 4];
// Checking for condition in array
var
value = array.some(isGreaterThan5);
document.write(value);
}
func();
</script>
- Output:
true
2. reduce() Method: The array reduce() method in JavaScript is used to reduce the array to a single value and executes a provided function for each value of the array (from left-to-right) and the return value of the function is stored in an accumulator.
- Example:
<script>
// Original array
var
numbers = [88, 50, 25, 10];
// Performing reduce method
var
sub = numbers.reduce(geeks);
function
geeks(total, num) {
return
total - num;
}
document.write(sub)
</script>
- Output:
3
3. map() Method: The map() method in JavaScript create an array by calling a specific function on each element present in the parent array. It is a non-mutating method. Generally, the map() method is used to iterate over an array and calling the function on every element of an array.
- Example:
<script>
// Original array
var
numbers = [4, 9, 16, 25];
// Performing map method
var
sub = numbers.map(geeks);
function
geeks() {
return
numbers.map(Math.sqrt);
}
document.write(sub)
</script>
- Output:
2, 3, 4, 5
4. every() Method: This method checks whether all the elements of the array satisfy the given condition or not that is provided by a function passed to it as the argument.
- Example:
<script>
// JavaScript code for every() function
function
ispositive(element, index, array) {
return
element > 0;
}
function
func() {
var
arr = [ 11, 89, 23, 7, 98 ];
// Check for positive number
var
value = arr.every(ispositive);
document.write(value);
}
func();
</script>
- Output:
true
5. flat() Method: This method creates a new array that contains more than arrays. Basically creates a simple array from an array that contains multiple arrays.
- Example:
<script>
//Original array
var
arr = [ [11, 89], [23, 7], 98 ];
// Performing flat method
var
geeks = arr.flat();
document.write(geeks)
</script>
- Output:
11, 89, 23, 7, 98
6. flatMap() Method: This method is used to flatten the input array element into a new array. This method first of all map every element with the help of mapping function, then flattens the input array element into a new array.
- Example:
<script>
const myAwesomeArray = [[1], [2], [3], [4], [5]]
var
geeks = myAwesomeArray.flatMap(arr => arr * 10)
console.log(geeks);
</script>
- Output:
10, 20, 30, 40, 50
7. filter() Method: This method is used to create a new array from a given array consisting of only those elements from the given array which satisfy a condition set by the argument function.
- Example:
<script>
function
isPositive(value) {
return
value > 0;
}
function
func() {
var
filtered = [112, 52, 0, -1, 944]
.filter(isPositive);
document.write(filtered);
}
func();
</script>
- Output:
112, 52, 944
8. findindex() Method: This method returns index of the first element in a given array that satisfies the provided testing function. Otherwise -1 is returned.
- Example:
<script>
var
array = [ 10, 20, 30, 110, 60 ];
function
finding_index(element) {
return
element > 25;
}
document.write(array.findIndex(finding_index));
</script>
- Output:
2
9. find() Method: This method is used to get the value of the first element in the array that satisfies the provided condition. It checks all the elements of the array and whichever the first element satisfies the condition is going to print.
- Example:
<script>
// Input array contain some elements.
var
array = [10, 20, 30, 40, 50];
// Function (return element > 10).
var
found = array.find(
function
(element) {
return
element > 20;
});
// Printing desired values.
document.write(found);
</script>
- Output:
30
10. fill() Method: This method used to fill the array with a given static value. The value can be used to fill the entire array or it can be used to fill a part of the array.
- Example:
<script>
// JavaScript code for fill() function
function
func() {
var
arr = [1, 23, 46, 58];
// Here value = 87, start index = 1 and
// and last index = 3
arr.fill(87, 1, 3);
document.write(arr);
}
func();
</script>
- Output:
1, 87, 87, 58
11. forEach() Method: This method calls the provided function once for each element of the array. The provided function may perform any kind of operation on the elements of the given array.
- Example:
<script>
function
func() {
// Original array
const items = [1, 29, 47];
const copy = [];
items.forEach(
function
(item){
copy.push(item*item);
});
document.write(copy);
}
func();
</script>
- Output:
1, 841, 2209
12. sort() Method: This method is used to sort the array. An array can be of any type i.e. string, numbers, characters etc.
- Example:
<script>
// Original array
var
numbers = [88, 50, 25, 10];
// Performing sort method
var
sub = numbers.sort(geeks);
function
geeks(a, b) {
return
a - b;
}
document.write(sub)
</script>
- Output:
10, 25, 50, 88
13. concat() Method: This method is used to merge two or more arrays together. This function does not alter the original arrays passed as arguments.
- Example:
<script>
// JavaScript code for concat() function
function
func() {
var
num1 = [11, 12, 13],
num2 = [14, 15, 16],
num3 = [17, 18, 19];
document.write(num1.concat(num2, num3));
}
func();
</script>
- Output:
11, 12, 13, 14, 15, 16, 17, 18, 19
14. includes() Method: This method is used to know either a particular element is present in the array or not and accordingly, it returns true or false i.e, if the element is present, then it returns true otherwise false
- Example:
<script>
// Taking input as an array A
// having some elements.
var
A = [ 1, 2, 3, 4, 5 ];
// Include() function is called to
// test whether the searching element
// is present in given array or not.
a = A.includes(2)
// Printing result of function.
document.write(a);
</script>
- Output:
true
15. reverse() Method: This method is used for in-place reversal of the array. The first element of the array becomes the last element and vice versa.
- Example:
<script>
function
func() {
//Original Array
var
arr = [34, 234, 567, 4];
document.write(
"Original array: "
+ arr);
//Reversed array
var
new_arr = arr.reverse();
document.write(
"<br>Newly reversed array: "
);
document.write(new_arr);
}
func();
</script>
- Output:
Original array: 34, 234, 567, 4 Newly reversed array: 4, 567, 234, 34