loops.txt

WHILE LOOP

// Setup
var myArray = [];

var n = 5;
while(n >= 0) {
    myArray.push(n);
    n--;
}

// results in myArray = [5, 4, 3, 2, 1, 0];

FOR LOOP

--odd number increment += 2, or decrement -= 2
// Setup
var myArray = [];

for (var n = 1; n < 10; n += 2) {
    myArray.push(n);
}

--iterate through array
// Setup
var myArr = [ 2, 3, 4, 5, 6];

var total = 0;
for (var n = 0; n < myArr.length; n++) {
    total += myArr[n];
}

//result:
total + myArr[0] -> 0 + 2 = 2 
total + myArr[1] -> 2 + 3 = 5
total + myArr[2] -> 5 + 4 = 9
total + myArr[3] -> 9 + 5 = 14 
total + myArr[4] -> 14 + 6 = 20

--NESTED LOOPS, MULTI-DIMENSIONAL ARRAYS--
function multiplyAll(arr) {
  var product = 1;

for (var n = 0; n < arr.length; n++) {
  for (var u = 0; u < arr[n].length; u++) {
    product = product * arr[n][u];
  }
}
  return product;
}

multiplyAll([[1,2],[3,4],[5,6,7]]);

---DO...WHILE LOOP-----
// Setup
var myArray = [];
var i = 10;


 do {
  myArray.push(i);
  i++;
} while (i < 11)

//result myArray = [10], code only runs once. Use this to make sure code runs at least once.

--EXCLUDE ARRAYS WITH ELEMENT FILTER ARGUEMENT
function filteredArray(arr, elem) {
  let newArr = [];
  for (let i = 0; i < arr.length; i++) {
  if (arr[i].indexOf(elem) == -1) {
    newArr.push(arr[i]);
  }
}
  return newArr;
}

console.log(filteredArray([[3, 2, 3], [1, 6, 3], [3, 13, 26], [19, 3, 9]], 3));

//returns [] -- all arrays have the element

--USERS ONLINE COUNT WITH FOR...IN-----
function countOnline(usersObj) {
  let count = 0;
  for (let user in usersObj) {
    if (usersObj[user].online === true) {
  count++;
    }
  } return count;
}