Loops

while

A while loop repeatedly executes a code block as long as a specified condition is true.

Some condition inside the code block will change, making the condition true.

var i = 0;
while (i < 5) {
  console.log("i is " + i);
  i++;
}

// Will print out:
// >i is 0
// >i is 1
// >i is 2
// >i is 3
// >i is 4

The parts of a while loop

while (CONDITION) {
  //CODE
}

var i=0;

while (i < 5) {

  console.log("i is " + i);

  i++;
}

Loop that runs forever

while(true){
  //CODE
}

Backwards Loops

It's totally possible to run the loop backwards. We need to do three things:

1. Instead of starting i at zero. We have to subtract one each iteration of the loop.
2. Change the test condition to run the for loop while i > 0
3. Change the step instruction to i--

var i=9;

while (i > 0) {

  i--;

  console.log("i is " i);
}

Exercise: Run some loops (10 mins)

• Setup Your Files (html / script)
• Copy the above code examples
• Change the value of i to something bigger
• Change the condition from less than to less than or equal to - what happens?
• Change the starting value of i to something else. What happens?
• Make a while loop that runs 1000 times and console.logs out i.
• Make a while loop that runs 1000 times and console.logs out hello
• Make a backwards loop
• Make a loop that increments more than one (counting forwards and backwards)
• Make a loop that runs a random amount of times (up to a reasonable number) - just google how to create a random integer in javascript if you don't know how.
• Crash your chrome browser tab by running a while loop that console.logs something and goes on forever.