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Fistly, What foes forEach method do
forEach() method iterates a given array and invoke a void function for all elements inside given array.

Arrow function:

let users = ['Burak', 'Hamdi', 'Tufan'];
users.forEach(element => {
  //some logic
});

Function calling with single parameter

let users = ['Burak', 'Hamdi', 'Tufan'];
function printFnc(el) {
    //some logic
}
users.forEach(myFunction);

Function calling with all array parameters

let users = ['Burak', 'Hamdi', 'Tufan'];
function printFnc(item, index, arr) {
    arr[index] = 'Hello ' + item;
}
function printFnc(el) {
    //some logic
}

In this usage, index and arr parameters are optional.

Below example controls all elements in array and print if even number.

let numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
numbers.forEach(element => {
  if(element % 2 === 0)
     console.log(element);
});

2
4
6
8
10

Below example you will see an example of forEach method. In this example we handled a JSON object with our declared method. We printed all of objects in aircrafts array.

let aircrafts = [
     {brand: "Airbus", model: "A330"}, 
     {brand: "Boeing", model: "777-300ER"}, 
     {brand: "Airbus", model: "A320"},
     {brand: "Boeing", model: "737-MAX9"}
];
function printAircraft(el) {
    console.log("Aircraft : " + el.brand + " " + el.model);
}
aircrafts.forEach(printAircraft);

Aircraft : Airbus A330
Aircraft : Boeing 777-300ER
Aircraft : Airbus A320
Aircraft : Boeing 737-MAX9

Below code block we will reverse an array. We will use the array item length and its index with forEach function. In this usage we used the optional index and arr parameters

let employees = [
    {name: "Burak", surname: "Tufan"}, 
    {name: "John", surname: "Doe"}, 
    {name: "Jane", surname: "Doe"}, 
    {name: "Albert", surname: "Einstein"}, 
    {name: "Nicola", surname: "Tesla"}, 
];

let reversedEmployees = [];

function relocateItem(item, index, arr) {
    reversedEmployees[arr.length -1 - index] = item;
}
employees.forEach(relocateItem);
console.log(reversedEmployees);

[
  { name: 'Nicola', surname: 'Tesla' },
  { name: 'Albert', surname: 'Einstein' },
  { name: 'Jane', surname: 'Doe' },
  { name: 'John', surname: 'Doe' },
  { name: 'Burak', surname: 'Tufan' }
]

let total = 0;
const numbers = [85,45,23,96,54,11,55,6524,3941,4,55,66,33,4,5,9,7,17,85,32,455,698,10,85,74,36,41,52,999];
console.log("For Method:" );
console.log("Start : " + window.performance.now());
for (let i = 0; i < numbers.length;i++)
     total += numbers[i];
console.log("End : " + window.performance.now());
console.log("ForEach Method:" );
total = 0;
console.log("Start : " + window.performance.now());
numbers.forEach(num => total += num);
var forEachEnd = window.performance.now();
console.log("End : " + window.performance.now());

For Method:
Start : 301202.7999999523
End : 301202.89999997616

ForEach Method:
Start : 301202.89999997616
End : 301202.89999997616

That is all in this article.

Have a good invokes for Each items.

Burak Hamdi TUFAN.