Unlike strongly typed languages, JavaScript does not enforce a return type on a function. This means that different paths through a function can return different types of values, which can be very confusing to the user and significantly harder to maintain.

In particular a function, in JavaScript, will return undefined in any of the following cases:

This rule verifies that return values are either always or never specified for each path through a function.

Noncompliant Code Example

function foo(a) { // Noncompliant, function exits without "return"
  if (a == 1) {
    return true;
  }
}

Compliant Solution

function foo(a) {
  if (a == 1) {
    return true;
  }
  return false;
}