Switch Statement Should Have a Default Case

javascript.default_case

Severity

info

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Best Practice

Language

JavaScript

Description

A switch statement without a default clause silently does nothing when the input does not match any of the listed case values:

// Bad — what happens for any other status?
switch (status) {
  case "open":   handleOpen();   break;
  case "closed": handleClosed(); break;
}

Rationale

Missing defaults are one of the most common sources of "the bug only happens in production" — a new enum value, a renamed status, an unexpected user input quietly falls through every branch. Adding a default forces the developer to make a deliberate decision about the unmatched case at the moment the switch is written.

Remediation

Add a default clause. If the unmatched case is genuinely impossible, throw or assert:

switch (status) {
  case "open":   handleOpen();   break;
  case "closed": handleClosed(); break;
  default:
    throw new Error("Unknown status: " + status);
}

If the unmatched case truly should be a silent no-op, an empty default clause documents that intent:

switch (status) {
  case "open":   handleOpen();   break;
  case "closed": handleClosed(); break;
  default: // intentionally ignored
}

Notes

The rule fires only when no default clause is present at all. A default: clause with an empty body is accepted because it shows the unmatched case was considered.

References

MDN — switch