JavaScript switch: Match Commands and Make Fall-Through Explicit

The task

Route two read-only commands to the same result, handle save separately and reject unrecognized types. The shared cases are deliberate, unlike an accidentally missing break after an action.

Runnable Node 22 example

const assert = require('node:assert/strict');

function route(command) {
  let action;
  switch (command) {
    case 'preview':
    case 'inspect': action = 'read'; break;
    case 'save': action = 'write'; break;
    case 1: action = 'numeric'; break;
    default: action = 'unknown';
  }
  return action;
}
assert.equal(route('preview'), 'read');
assert.equal(route('inspect'), 'read');
assert.equal(route('save'), 'write');
assert.equal(route(1), 'numeric');
assert.equal(route('1'), 'unknown');
console.log(['preview', 'save', '1'].map(route).join(','));

Expected output and explanation

preview reaches the read assignment through the intentionally shared case path. break prevents the save assignment from running afterward. The numeric case accepts 1 but not the string “1,” making the comparison boundary visible.

The default supplies a defined result for an unrecognized command. This example returns an action label rather than performing storage or granting permission; routing to write is not itself an authorization check.

Pitfall to check

If cases declare let or const variables with the same name, use case-local braces where separate block scope is required. Also test unknown values: forgetting a default can leave an action unset even when the known cases work.