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forEach() method calls a function for each element in an array.

Function Proto-type 1:

Array.forEach( function(currentValue, index, arr) {
	...
} );

Function Proto-type 2: simplified version

Array.forEach( function(currentValue) {
	...
} );

Example 1) Compute the sum:

let sum = 0;
const numbers = [ 65, 44, 12, 4 ];

numbers.forEach( function(item) {
	sum += item;
});

Example 2) Compute the sum:

let sum = 0;
const numbers = [ 65, 44, 12, 4 ];

numbers.forEach( myFunction);

function myFunction(item)
{
	sum += item;
}

Example 3) Multiple each element:

let sum = 0;
const numbers = [ 65, 44, 12, 4 ];

numbers.forEach( function(item, idx, arr) {
	arr[idx] = item * 10;
});