Deeply nested if statements are hard to read and so to maintain.

The following code snippet illustrates this rule with the default threshold of 3 :

function sayHello() {
  if (true) {
    if (true) {
      if (true) {
        if (true) { // Non-Compliant
          return;
        } else {
          return;
        }
      } else if (true) { // Compliant
        if (true) { // Non-Compliant
          return;
        }
      }
    }
  }
}