If/Else Statements

Now we're going to start adding in some logic. So far we have been logging the same thing every time we run the code, but what if we want to log according to different conditions? In programming there is something called an "if/else statement". It tests conditions, and will perform different actions based on the outcome of these tests.

The structure of an if/else statement in JavaScript is as follows:

if (condition) {
  // do something
} else {
  // do something else
}

It basically translates to "if this condition is true, do this - or else do something else".

Try it out

What if we want to console.log() "Hello world!" if we're feeling happy, and something else if we're sad?

Let's define a variable called isHappy, and assign it a boolean value of true or false (depending on how happy you're feeling).

var isHappy = true;

Then let's write our if/else statement. In our condition, we want to test if the variable isHappy is equal to true. Note that in JavaScript, to test if two things are equal you need to use a triple equals (===) rather than just one (=).

if (isHappy === true) {
  // do something
} else {
  // do something else
}

Now let's add in what will happen if the conditions are met. The comments are there to explain what is happening.

if (isHappy === true) {
  // if I am happy, print "Hello world!"
  console.log('Hello world!');
} else {
  // if I am sad, print a frowny face
  console.log(':(');
}

Now run this code and see what happens! Try changing the value of your variable from true to false.

Exercise

Write an if/else statement that evaluates if a number is even or odd. If it is even, it will print the string 'even', and if it is odd, it will print 'odd'.

For this challenge, you might find it useful to use the "modulo" operator, which looks like this: %. The modulo operator finds the remainder after division of one number by another. For example:

13 % 2 === 1 // 13 divided by 2 leaves a remainder of 1
100 % 10 === 0 // 100 divided by 10 leaves a remainder of 0

Exercise

Now improve your code so that it prints out if the number is positive or negative, as well as even or odd. For example, for -5 it will print 'negative odd', while for 4 it will print 'positive even'.

Hint: You can use the > or < signs.

If you finish early, think about how you would test your code works correctly?