While Loop

While Loops repetitively execute a block of code as long as a specified condition is true.

while (condition) {
  // do it as long as condition is true
}

For example, the loop in this example will repetitively execute its block of code as long as the variable i is less than 5:

var i = 0,
  x = "";
while (i < 5) {
  x = x + "The number is " + i;
  i++;
}

Note: Be careful to avoid infinite looping if the condition is always true!

{% exercise %} Using a while-loop, create a variable named message that equals the concatenation of integers (0, 1, 2, …) as long as its length (message.length) is less than 100. {% initial %} var message = “”; {% solution %} var message = “”; var i = 0;

while (message.length < 100) { message = message + i; i = i + 1; } {% validation %} var message2 = “”; var i2 = 0;

while (message2.length < 100) { message2 = message2 + i2; i2 = i2 + 1; } assert(message === message2); {% endexercise %}