Imagine someone telling you to pick up a few things at the grocery store:
"Go to the Safeway at 50th and Brooklyn in the U-District by the Jack in the Box and pick us up a gallon of milk. Oh, also, while you're at the Safeway at 50th and Brooklyn in the U-District by the Jack in the Box you should also buy a 12-pack of Mountain Dew. It's a fun errand. The cashier guy at that Safeway at 50th and Brooklyn in the U-District by the Jack in the Box is hilarious."
Wow. Why did they have to tell us exactly where it is so many times? We got the idea the first time they clarified it. Although it's easy to see that telling someone the exact location of a Safeway several times in conversation is unnecessary in a conversation, it's easy to make the same sort of mistake in programming.
Learning Objectives
define redundancy
identify examples of redundancy
see how to reduce redundancy
practice reducing redundancy
What is Redundany?
Redundancy is any code that repeats itself unnecessarily. Redundant code can take a long time to write. Redundant code exposes programs to silly errors, like increasing the likelihood of making a typo when you type something several times, or making a change in 9/10 places, but forgetting to make a change in the last tenth place.
Programmers like to reduce redundancy for several reasons:
code becomes easier to read
code becomes easier to maintain
code may become more efficient because a computer doesn't have to
process identical operations over and over again.
it's easier to make changes to
changes made in just one place are guaranteed to be consistently the same.
sometimes programmers just like to write code because it's shorter and
faster to write!
Here's a collection of several examples of redundant code and what you can do to prevent redundancy.
Flipping Boolean Values
It's super common to flip a boolean value back and forth between true and false. Instead of using a four-line if/else structure, you can use the not operator to turn true into false and false into true. Here's your options:
for (var i = 0; i < 9; i++) {
document.getElementById("cell" + i).textContent="";
document.getElementById("cell" + i).style.backgroundColor= "white";
}
Factoring if/else Branches
Whenever a piece of code appears in every branch of an if/else if/else statement we can factor it out so it appears just once immediately after the entire if statement.
Think of this like reducing a common denominator from a fraction. If every branch of an if/else statement is "divisible" by a statement then the statement can be "factored out" and written just just before or after the entire if/else statement.
These two functions repeat code defining how to set a background image. We can make a third function that accepts a parameter representing The filename to be used as the background image, and each of the original functions can pass in their filename to the old function.
If you're copying and pasting strings, you're probably writing redundant code. In this example we can save ourselves from writing a string twice. Instead of writing on both sides of an if/else statement we write it once at the end. The two parts of it that changes are saved as values in variables.
Create a function that creates an image tag and appends it to an element. The function should be parameterized so it can accept an id of the element to attach the image to, and second parameter for the filename of the iamge.
