New rule proposal: default-case-last

[mdjermanovic]

Please describe what the rule should do:

Enforce default clauses in switch statements to be last.

What category of rule is this? (place an "X" next to just one item)

[X] Suggests an alternate way of doing something (suggestion)

Provide 2-3 code examples that this rule will warn about:

switch (foo) {
  case 1:
    bar();
    break;
  default:
    baz();
    break;
  case 2:
    quux();
    break;    
}

switch (foo) {
  default:
    doSomethingForNonZero();
    // fallthrough
  case 0:
    doSomethingForAll();
    break;
}

Why should this rule be included in ESLint (instead of a plugin)?

This rule enforces a common convention.

Even if a non-last default might make sense for a specific situation, it's better to refactor the code to a more understandable version.

A non-last default is, I believe, unexpected for readers. A reader might not know if it is a valid code at all, and what's the actual behavior (does the evaluation stop when it finds default in the middle, does it execute the default block and then continue searching, etc.).

This rule applies only to switch statements that already have default clauses. It doesn't enforce the existence of default clauses (there is the default-case rule for that purpose).

Are you willing to submit a pull request to implement this rule?

Yes.

[platinumazure]

I didn't even know this was allowed in JS. Yes, we should definitely create a rule for enforcing this!

[mdjermanovic]

I'm working on this.

[shirohana]

Hi there,

I found that the rule default-case-last hasn't be linked correctly in https://eslint.org/docs/rules/default-case-last but shows in https://eslint.org/docs/rules/#best-practices, is it in a plan to be update or just a bug (´・ω・｀)?

[kaicataldo]

This is a bug in our website generator for prerelease versions. Sorry about that!