While Loop

Loop condition is evaluated before loop start.

while(condition){
   //...
}

Auto-guess a number between 1-10000

var upper = 10000
var attempts = 0;
var guess;
var num = parseInt(prompt("Enter a number between 1 and 10000"));

function getRandomNumber (upper) {
  return Math.floor( Math.random() * upper ) + 1;
}

while( guess !== num ){
  guess = getRandomNumber(upper);
  attempts += 1;
}
document.write( "Number is "+ num +"<br>");
document.write( "Number of guesses is "+ attempts );

Do-While Loop

Loop condition isn NOT evaluated until code block is run once.

do {
  //...
} while(condition)

Guess a number between 1-10

var num = getRandomNumber(10);
var guess;
var attempts = 0;
var correctGuess = false;

function getRandomNumber (upper) {
  return Math.floor( Math.random() * upper ) + 1;
}

do {
  guess = prompt("What's the number?");
  attempts += 1;
  if ( num === parseInt(guess) ){
    correctGuess = true;
  }
} while( !correctGuess )
document.write("Correct! Number of guesses is "+ attempts);

For-Loop

for(var i=0; i < 10; i+=1){
  //...
}

Example

for(var i = 4; i <= 156; i += 1 ){
  document.write(i);
}

for (var j = 0; j <= 100; j += 10) {
  console.log( j );
}
// Code will be executed 11 times – j: 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100.