How to forEach Over an Array in JavaScript

 Use the forEach() Method

You can simply use the array's forEach() method to loop through all the items in an array using JavaScript. The forEach() method executes a provided function once for each array element.

The following example will display all the values in the cities array using foreach loop.

<script>
    // Sample array
    var cities = ["London", "Paris", "New York", "Amsterdam"];
    
    // Loop over array
    cities.forEach(function(value){
        document.write("<p>" + value + "</p>");
    });
</script>

The forEach() method does not modify the original array (i.e. the array on which it is called). However, the callback function, if invoked, may do so. The following example will modify the given array by squaring each of its value (multiplying it by itself).

<script>
    // Sample array
    var numbers = [1, 2, 3, 4, 5, 6];
    
    // Loop over array and squaring each value
    numbers.forEach(function(value, index, array){
        array[index] = value * value;
    });
    
    console.log(numbers); // Prints: [1, 4, 9, 16, 25, 36]
</script>