Tip 1: Signal Unchanging Values With const
Which variable declaration to use?
In the past, you had only one option for non-global variable assignment:
Now there are many different options—
const—and each one has
an appropriate usage. Try and keep things simple. In most cases,
const is the
best choice, not because it allows you to do the most, but because it lets you
do the least. It has restrictions that make your code more readable.
const is a variable declaration that you can’t reassign within the context of the
block. In other words, once you establish it, it can’t be changed. That doesn’t
mean it’s immutable—a value that cannot be changed. If it’s assigned to an
array, the items in the array can be changed. We’ll look at this more shortly.
It may seem odd to developers in other languages with a constant assignment
const is the preferred declaration. In those languages, a constant is usually
something you’d write in ALLCAPS and only use on rare occasions to
denote things that are never going to change, like the first digits of pi.
const is a great default choice precisely because it can’t be reassigned. When you assign a value, you aren’t just declaring a piece of information. You’re also signaling what you plan to do with that information. When you assign values and signal that they won’t be changed, you give future developers (including yourself!) the knowledge that they can forget about a value while they skim the code. And when you’re reading a large amount of code that you haven’t seen before, you’ll be happy that you can
forget some of what you read.
Let’s assume you’re fixing a bug in a piece of code. You’re skimming through the code to get an idea of how it works and to see if you can guess where the problem might be.
Consider two programs. The first program uses
const to assign a variable.