en.javascript.info/1-js/02-first-steps/13-switch/2-rewrite-if-switch/solution.md

The first two checks turn into two case. The third check is split into two cases:

let a = +prompt('a?', '');

switch (a) {
  case 0:
    alert( 0 );
    break;

  case 1:
    alert( 1 );
    break;

  case 2:
  case 3:
    alert( '2,3' );
*!*
    break;
*/!*
}

Please note: the break at the bottom is not required. But we put it to make the code future-proof.

In the future, there is a chance that we'd want to add one more case, for example case 4. And if we forget to add a break before it, at the end of case 3, there will be an error. So that's a kind of self-insurance.