noFallthroughCasesInSwitch - explicitly allow fall through

user_4552651 0
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  1. I've enabled the noFallthroughCasesInSwitch option in the tsconfig.json file.
  2. That option warned me about an "error", and I want to let the Typescript compiler know it's intentional.
  3. It's not documented, and the online examples don't work for me - how can I mark it as intentional?
function getRandomInt(max: number) {
  return Math.floor(Math.random() * max);
}

switch(getRandomInt(3)) {
  /* falls through */
  /* fall through */
  /* FALLTHROUGH */
  case 1: /* falls through */ /* fall through */ /* FALLTHROUGH */ /* <----- Still getting an error here "Fallthrough case in switch. (7029)" */
    /* falls through */
    /* fall through */
    /* FALLTHROUGH */
    console.log(1);
    /* falls through */
    /* fall through */
    /* FALLTHROUGH */
  case 2:
    console.log(2);
    break;
}

The error can be seen in this link as well: link. But there's a bug in TS Playground, so you must manually click the "TS Config" menu and then Tick the noFallthroughCasesInSwitch option so it will be turned on, otherwise, you'll not see the error.

typescript switch-statement
2 Answers

Three options:

1 - Use @ts-ignore to suppress the error

As you did, I would always include a comment being explicit about it as well, including what case it falls through to:

function getRandomInt(max: number) {
  return Math.floor(Math.random() * max);
}

switch(getRandomInt(3)) {
  // @ts-ignore
  case 1:
    console.log(1);
    // FALLS THROUGH to 2
  case 2:
    console.log(2);
    break;
}

2 - Use @ts-expect-error (TypeScript 3.9+)

Or with TypeScript 3.9 you might use @ts-expect-error so that if someone edits the code (or config) to make the error go away, TypeScript warns you about it:

function getRandomInt(max: number) {
  return Math.floor(Math.random() * max);
}

switch(getRandomInt(3)) {
  // @ts-expect-error
  case 1:
    console.log(1);
    // FALLS THROUGH to 2
  case 2:
    console.log(2);
    break;
}

3 - Don't fall through

Alternatively, stack the labels so the case 1 label is empty (it still falls through, but TypeScript's noFallthroughCasesInSwitch only gets triggered by non-empty case labels that fall through, not stacked ones [empty ones followed by non-empty ones]):

function getRandomInt(max: number) {
  return Math.floor(Math.random() * max);
}

const n = getRandomInt(3);
switch(n) {
  case 1:
  case 2:
    if (n === 1) {
      console.log(1);
    }
    console.log(2);
    break;
}
user_1572470

The way I finally solved it: I've disabled the noFallthroughCasesInSwitch option in the tsconfig.json file and installed ESLint instead.

TypeScript does very little linting, and used to have TSLint as a complementary linter, which is now deprecated and replaced by ESLint.

My personal opinion is that TypeScript should not suggest by themselves any changes to the code that is not expected to fail their build process, and they should use a 3rd-party linting tool like ESList. Doing only some linting - leads to non-polished rules and problems like my question above.

user_45526510
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