5.5. Nested Conditionals¶

We can write code with more complex branching behavior by combining conditionals and, in particular, by nesting conditionals. Let's see how this works by tackling the following problem.

Our first attempt at a solution might look like this:

1let num = 7;
2
3if (num % 2 === 0) {
4   console.log("EVEN");
5}
6
7if (num > 0) {
8   console.log("POSITIVE");
9}

Console Output

POSITIVE

We find that the output is POSITIVE, even though 7 is odd and so nothing should be printed. This code doesn't work as desired because we only want to test for positivity when we already know that the number is even. We can enable this behavior by putting the second conditional inside the first.

1let num = 7;
2
3if (num % 2 === 0) {
4    console.log("EVEN");
5
6    if (num > 0) {
7        console.log("POSITIVE");
8    }
9}

repl.it

Notice that when we put one conditional inside another, the body of the nested conditional is indented by two tabs rather than one. This convention provides an easy, visual way to determine which code is part of which conditional.

1let num = 7;
2
3if (num % 2 === 0) {
4    if (num % 2 === 1) {
5        console.log("odd");
6    }
7}

1if (num % 2 === 0) {
2    if (num % 2 === 1) {
3        console.log("odd");
4    }
5}