Ways of iterating over a array in JavaScript
In this article, we will learn, we will learn how to iterate over an array using JavaScript, there are multiple ways to do so. Arrays in Javascript, are single variables used to store different kinds of elements.
- using for loop
- using while loop
- using forEach() Method
- using every() Method
- using reduce() Method
- using some() Method
Example: Simple array access may be something like this.
javascript
array = [ 'geeks' , '4' , 'geeks' ]; // Accessing array elements one by one console.log(array[0]); console.log(array[1]); console.log(array[2]); |
Output:
geeks 4 geeks
There are multiple ways one can iterate over an array in Javascript. The most useful ones are mentioned below.
Example using for loop: This is similar to for loops in other languages like C/C++, Java, etc.
javascript
array = [1, 2, 3, 4, 5, 6]; for (index = 0; index < array.length; index++) { console.log(array[index]); } |
Output:
1 2 3 4 5 6
Example using while loop: This is again similar to other languages.
javascript
index = 0; array = [1, 2, 3, 4, 5, 6]; while (index < array.length) { console.log(array[index]); index++; } |
Output:
1 2 3 4 5 6
Example using forEach() Method: The forEach method calls the provided function once for every array element in the order.
javascript
index = 0; array = [1, 2, 3, 4, 5, 6]; array.forEach(myFunction); function myFunction(item, index) { console.log(item); } |
Output:
1 2 3 4 5 6
Example using every() Method: The every() method checks if all elements in an array pass a test (provided as a function).
javascript
index = 0; array = [1, 2, 3, 4, 5, 6]; const under_five = x => x < 5; if (array.every(under_five)) { console.log( 'All are less than 5' ); } else { console.log( 'At least one element is not less than 5' ); } |
Output:
At least one element is not less than 5.
Example using map() Method: A map applies a function over every element and then returns the new array.
javascript
index = 0; array = [1, 2, 3, 4, 5, 6]; square = x => Math.pow(x, 2); squares = array.map(square); console.log(array); console.log(squares); |
Output:
1 2 3 4 5 6 1 4 9 16 25 36
Example using Filter() Method: It is used to filter values from an array and return the new filtered array
Javascript
array = [1, 2, 3, 4, 5, 6]; even = x => x % 2 === 0; evens = array.filter(even); console.log(array); console.log(evens); |
Output:
[ 1, 2, 3, 4, 5, 6 ] [ 2, 4, 6 ]
Example using reduce() Method: It is used to reduce the array into one single value using some functional logic
Javascript
array = [1, 2, 3, 4, 5, 6]; const helperSum = (acc, curr) => acc + curr sum = array.reduce(helperSum, 0); console.log(array) console.log(sum); |
Output:
[ 1, 2, 3, 4, 5, 6 ] 21
Example using some() Method: It is used to check whether some array values pass a test
Javascript
array = [1, 2, 3, 4, 5, 6]; const lessthanFourCheck = (element) => element < 4; const lessthanFour = array.some(lessthanFourCheck) console.log(array); if (lessthanFour) { console.log( "At least one element is less than 4" ) } else { console.log( "All elements are greater than 4 " ) } |
Output:
[ 1, 2, 3, 4, 5, 6 ] At least one element is less than 4
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