The most common type of JavaScript loop is called a for loop because it runs for a specific number of times.

var ourArray = [];
for(var i = 0; i < 5; i++) {
  ourArray.push(i);
}

ourArray will now contain [0,1,2,3,4]

for(var i = 0; i < 5; i++) {  // There are 3 parts here

There are three parts to for loop. They are separated by semicolons.

1. The initialization: var i = 0; - This code runs only once at the start of the loop. It's usually used to declare the counter variable (with var) and initialize the counter (in this case it is set to 0).

2. The condition: i < 5; - The loop will run as long as this is true. That means that as soon as i is equal to 5, the loop will stop looping. Note that the inside of the loop will never see i as 5 because it will stop before then. If this condition is initially false, the loop will never execute.

3. The increment: i++ - This code is run at the end of each loop. It's usually a simple increment (++ operator), but can really be any mathematical transformation. It is used to move the counter (i) forward (or backwards, or whatever.