For Loop 
for (expression 1; expression 2; expression 3) {
  // code block to be executed }

for (let i = 0; i < 5; i++) {
  text += "The number is " + i + "<br>";
}

Loops can execute a block of code a number of times. For loops use three expressions. A starting point, conditional, and an iteration.

Loops JS
Nested Loops 
const array1 = [6, 19, 20];
const array2 = [19, 81, 2];

for (let i = 0; i < array1.length; i++) {
  for (let j = 0; j < array2.length; j++) {
    if (array1[i] === array2[j]) {
      console.log('Both arrays have the number: ' + array2[j]); 
    }
  }
}

For each round of the outer for loop, the inner for loop will run completely.

Loops JS
break 
let i = 0;

while (i < 6) {
  if (i === 3) {
    break;
  }
  i = i + 1;
}

console.log(i); // Expected output: 3

Breaks out of a loop if executed.

Loops JS
For In Loop 
const object = { a: 1, b: 2, c: 3 };

for (const property in object) {
  console.log(`${property}: ${object[property]}`);
}

// Expected output:
// "a: 1"
// "b: 2"
// "c: 3"

The javascript for in statement loops through the properties of objects and arrays.

Loops JS
While Loop 
let n = 0;

while (n < 3) {
  n++;
}

console.log(n);
// Expected output: 3

Runs while a condition is true.

Loops JS
continue 
let text = '';

for (let i = 0; i < 10; i++) {
  if (i === 3) {
    continue;
  }
  text = text + i;
}

console.log(text); // Expected output: "012456789"

"Jumps over" one iteration in a loop and continues.

Loops JS
For Of Loop 
const array1 = ['a', 'b', 'c'];

for (const element of array1) {
  console.log(element);
}

// Expected output: "a"
// Expected output: "b"
// Expected output: "c"

Loops through the values of an iterable object, Arrays, Strings, Maps, NodeLists, and more.

Loops JS
Do While Loop 
let result = '';
let i = 0;

do {
  i = i + 1;
  result = result + i;
} while (i < 5);

console.log(result);
// Expected output: "12345"

Creates a loop that executes until a condition evaluates to false.

Loops JS