Arrays in JavaScript have several methods for filtering, mapping or folding that require a callback. Not having a return statement in such a callback function is most likely a mistake.

This rule applies for the following methods of an array:

Noncompliant Code Example

var merged = arr.reduce(function(a, b) {
  a.concat(b);
}); // Noncompliant: No return statement

Compliant Solution

var merged = arr.reduce(function(a, b) {
  return a.concat(b);
});