forEach()

forEach = method used to iterate over the elements of an array and apply a specified function(callback) to each element.

• array.forEach(callback)

let numbers = [1, 2, 3, 4, 5];
 
numbers.forEach(display); // each element in the array execute the function
function display(element){
	console.log(element); // output:all the element in array
}
 
 
numbers.forEach(double); // now the output number will double
function double(element, index, array){
	array[index] = element * 2;
}
function triple(element, index, array){
	array[index] = element * 3;
}
function square(element, index, array){
	array[index] = Math.pow(element, 2);
}
function cube(element, index, array){
	array[index] = Math.pow(element, 3);
}

More practical example:

let fruits = ["apple", "orange", "banana", "coconut"];
 
fruits.forEach(upperCase);
fruits.forEach(lowercase);
fruits.forEach(capitalize);
fruits.forEach(display);
 
function upperCase(element, index, array){
	array[index] = element.toUpperCase();
}
 
function lowercase(element, index, array){
	array[index] = element.toLowerCase();
}
 
function capitalize(element, index, array){
	array[index] = element.charAt(0).toUppercase() + element.slice(1);
}
 
function display(element){
	console.log(element);
}