no-fallthrough.md

Pattern: Case statement without break or comment

Issue: -

Description

Switch statements in JavaScript allow case statements to fall through to the next case when there is no break, return, or throw. While this can be intentional, unmarked fallthroughs are often mistakes. Intentional fallthroughs should be marked with a comment containing "falls through" or similar.

Examples

Example of incorrect code:

switch (foo) {
  case 1:
    doSomething();
  case 2:
    doSomethingElse();
  default:
    cleanup();
}

Example of correct code:

switch (foo) {
  case 1:
    doSomething();
    break;
  
  case 2:
    doSomethingElse();
    // falls through
    
  default:
    cleanup();
}

switch (foo) {
  case 1:
  case 2:  // multiple cases sharing code is fine
    sharedOperation();
    break;
    
  case 3:
    return specialOperation();  // return also prevents fallthrough
}