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default-case

Some coding conventions require that all switch statements have a default case, even if empty.
Rule Type: Suggestion
Fixable: No

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Why This Rule Exists

Always having a default case makes it clear whether the developer forgot to handle a case or intentionally has no default behavior. 
switch (foo) {
    case 1:
        doSomething();
        break;
    case 2:
        doSomething();
        break;
    default:
        // do nothing
}

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Rule Details

This rule requires a default clause in switch statements. You can optionally include a // no default comment if there’s no default case.

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Examples

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Incorrect Code

switch (a) {
    case 1:
        /* code */
        break;
}

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Correct Code

// With default case
switch (a) {
    case 1:
        /* code */
        break;
    default:
        /* code */
        break;
}

// With comment indicating intentional omission
switch (a) {
    case 1:
        /* code */
        break;
    // no default
}

switch (a) {
    case 1:
        /* code */
        break;
    // No Default
}

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Options

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commentPattern

Type: string (regex)
Default: /^no default$/i Customize the comment pattern that indicates an intentional omission: 
{
  "rules": {
    "default-case": ["error", { 
      "commentPattern": "^skip\\sdefault" 
    }]
  }
}
Examples with custom pattern: 
switch(a) {
    case 1:
        /* code */
        break;
    // skip default
}

switch(a) {
    case 1:
        /* code */
        break;
    // skip default case
}

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Best Practices

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Explicit Default Handling

Even if the default does nothing, make it explicit to show it was considered.
// Good: Shows you thought about defaults
switch (userType) {
    case 'admin':
        grantAdminAccess();
        break;
    case 'user':
        grantUserAccess();
        break;
    default:
        // Unknown user type, no special access
        break;
}

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Error Handling in Default

// Handle unexpected values
switch (status) {
    case 'pending':
        showPending();
        break;
    case 'completed':
        showCompleted();
        break;
    default:
        throw new Error(`Unknown status: ${status}`);
}

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Logging Unknown Cases

// Log for debugging
switch (action.type) {
    case 'INCREMENT':
        return state + 1;
    case 'DECREMENT':
        return state - 1;
    default:
        console.warn(`Unknown action type: ${action.type}`);
        return state;
}

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When Not to Use It

Disable this rule if you don’t want to require default cases or comments in switch statements.