Loops

- You may have noticed that so far in the course every thing we've done has focused on the singular. We've created variables, functions and objects, and added interactivity using events but all these things have been unique one off things. In the real world, that is rarely how things work and, in many cases, we specifically want our code to do things more than once, usually as many times as is necessary and sometimes even endlessly. For this, we have loops. Loops are quite literally loops.

We start a process, usually a function, then, when it's done, we start the process again. Loops are a vital part of all programming languages and will play a vital role in most JavaScript code you'll write, so, we'll dedicate a whole chapter to them. At their core, loops are simple. We create some sort of condition and say for as long as this condition holds, keep running the loop. The class A example of a loop looks like this. For (vari=0;i<10;i++){ and then we console.log(i).

When we run this, it'll spit out zero, one, two, three, four, five, six, seven, eight, nine, and then stop. If we break this apart, here's what happens. First, we step up a for loop which will run the core block inside the curly brackets for as long as the condition is true. Then, inside the condition area of the for loop, we set up a variable I for index or increments and assign zero to it. Then we check to see if I is smaller than 10, which it is, so the condition is true, and, finally, we add one to I.

This loop will run 10 times and then stop on its own. The for loop assumes you know how many times you want to loop to run but sometimes you just want to run the loop until some condition changes. In that case, you can use a while loop instead. This example does the exact same thing as the first one, looping through the same code 10 times, but here it tests a condition that is altered outside the while declaration.

The while loop allows us to create more advanced functions inside the core block and run the loop as long as these or other external conditions are true. A basic example of this would be to use a while loop to find out how many times we can exponentially grow 2.1 before it gets to 567. Run this code example in the console and you'll get nine repetitions. However, if we start it out with 567 as the value, it would never run and we wouldn't be told it only needs to run once.

To ensure the loop runs at least once, we have the do while loop. Here, we run the core block first and then check the while statement. Exactly what type of loop works best for your situation depends on, well, what type of loop you're creating. For loops are by far the most common but while and do while loops also have their uses and, in some cases, they're all interchangeable, it all depends.

The important thing is to remember you have options and each is slightly different from the next.