If you try to redeclare variables in a switch block then it will cause errors because there is only one block. For example, the below code block throws a syntax error as below,

let counter = 1;
switch (x) {
  case 0:
    let name;
    break;

  case 1:
    let name; // SyntaxError for redeclaration.
    break;
}

To avoid this error, you can create a nested block inside a case clause and create a new block scoped lexical environment.

let counter = 1;
switch (x) {
  case 0: {
    let name;
    break;
  }
  case 1: {
    let name; // No SyntaxError for redeclaration.
    break;
  }
}