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Ways of iterating over a array in JavaScript

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  • Last Updated : 03 Nov, 2022
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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.

Example: Simple array access may be something like this.

javascript




<script>
    array = [ 'geeks', '4', 'geeks' ];
      
    // Accessing array elements one by one
    console.log(array[0]);
    console.log(array[1]);
    console.log(array[2]);
</script>


Output: 

geeks
4
geeks

There are multiple ways one can iterate over an array in Javascript. The most useful ones are mentioned below.

Using for loop: This is similar to for loops in other languages like C/C++, Java, etc 

javascript




<script>
    array = [ 1, 2, 3, 4, 5, 6 ];
    for (index = 0; index < array.length; index++)
    {
        console.log(array[index]);
    }
</script>


Output:  

1
2
3
4
5
6

Using while loop: This is again similar to other languages. 

javascript




<script>
    index = 0;
    array = [ 1, 2, 3, 4, 5, 6 ];
      
    while (index < array.length) 
    {
        console.log(array[index]);
        index++;
    }
</script>


Output: 

1
2
3
4
5
6

Using forEach() Method: The forEach method calls the provided function once for every array element in the order. 

javascript




<script>
    index = 0;
    array = [ 1, 2, 3, 4, 5, 6 ];
      
    array.forEach(myFunction);
    function myFunction(item, index)
    {
        console.log(item);
    }
</script>


Output: 

1
2
3
4
5
6

Using every() Method: The every() method checks if all elements in an array pass a test (provided as a function). 

javascript




<script>
    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');
    }
</script>


Output: 

At least one element is not less than 5.

Using map() Method: A map applies a function over every element and then returns the new array. 

javascript




<script>
    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);
</script>


Output:

1 2 3 4 5 6 
1 4 9 16 25 36

Using Filter() Method: It is used to filter values from an array and return the new filtered array

Javascript




<script>
    array = [ 1, 2, 3, 4, 5, 6 ];
      
    even = x => x%2 === 0;
    evens = array.filter(even);
    console.log(array);
    console.log(evens);
</script>


Output:

[ 1, 2, 3, 4, 5, 6 ]
[ 2, 4, 6 ]

Using reduce() Method: It is used to reduce the array into one single value using some functional logic

Javascript




<script>
    array = [ 1, 2, 3, 4, 5, 6 ];
      
    const helperSum = (acc,curr) => acc+curr
    sum = array.reduce(helperSum, 0);
      
    console.log(array)
    console.log(sum);
</script>


Output:

[ 1, 2, 3, 4, 5, 6 ]
21

Using some() Method: It is used to check whether some array values pass a test

Javascript




<script>
    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 ")
     }
</script>


Output: 

[ 1, 2, 3, 4, 5, 6 ]
At least one element is less than 4

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