javascript function loop through array

1var data = [1, 2, 3, 4, 5, 6];
2
3// traditional for loop
4for(let i=0; i<=data.length; i++) {
5  console.log(data[i])  // 1 2 3 4 5 6
6}
7
8// using for...of
9for(let i of data) {
10	console.log(i) // 1 2 3 4 5 6
11}
12
13// using for...in
14for(let i in data) {
15  	console.log(i) // Prints indices for array elements
16	console.log(data[i]) // 1 2 3 4 5 6
17}
18
19// using forEach
20data.forEach((i) => {
21  console.log(i) // 1 2 3 4 5 6
22})
23// NOTE ->  forEach method is about 95% slower than the traditional for loop
24
25// using map
26data.map((i) => {
27  console.log(i) // 1 2 3 4 5 6
28})

1//function arrayLooper will loop through the planets array
2const planets = ["Mercury", "Venus", "Earth", "Mars"];
3
4const arrayLooper = (array) => {
5  for (let i = 0; i < array.length; i++) {
6    console.log(array[i]);
7  }
8};
9arrayLooper(planets);

1let fruits = ['Apple', 'Banana'];
2
3fruits.forEach(function(item, index, array) {
4  console.log(item, index);
5});
6// Apple 0
7// Banana 1

1fruits.forEach(function(item, index, array) {
2  console.log(item, index)
3})
4// Apple 0
5// Banana 1
6

1array iteration styles illustrate programming paradigms
2let newArray = [];  const theArray = [2, 4, 6, 8, 10]
3// 1) imperative, explicit
4for (var i = 0; i < theArray.length; i++) {  // var is mutable
5    console.log(theArray[i]);                // side effect from writing to console
6	newArray[i] = theArray[i] * theArray[i]  // let is mutable
7}
8// 2) forEach function of the Array class TIP: console.log(Array) //Does not change the array, Returns undefined
9function f1(theValue, theIndex, originalArray) { numVal = numVal *  theValue }
10theArray.forEach(f1);   console.log( ` creates  ${   newArray   }` );
11run.addEventListener("click", function () {cpeople.forEach((element) => console.log(element.firstname));});
12// 3) declarative, implicit 
13function f1(v,i,a) { v=v*v }
14const constArray = theArray.map(fNumbers); 
15console.log( ` immutable  ${ newArray }` );
16
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