eslint: no-case-declaration – unexpected lexical declaration in case block

eslint: no-case-declaration – unexpected lexical declaration in case block

If you’ve encountered the eslint: no-case-declaration error while working with JavaScript, you’re not alone. This error occurs when a lexical declaration (such as let, const, or class) is found within a case block. This is considered bad practice because case blocks are meant to contain executable statements, not variable declarations.

Fortunately, there are a few ways to resolve this error:

1. Move the declaration outside the case block

The simplest solution is to move the lexical declaration outside the case block. By doing so, you ensure that the declaration is executed before the switch statement is evaluated. Here’s an example:

let value;

switch (condition) {
  case 'A':
    value = 1;
    break;
  case 'B':
    value = 2;
    break;
  default:
    value = 0;
    break;
}

console.log(value);

In this example, we declare the value variable before the switch statement and assign its value within each case block. This ensures that the variable is properly initialized and avoids the eslint: no-case-declaration error.

2. Wrap the case block in a block statement

If you need to keep the lexical declaration within the case block for some reason, you can wrap the block in a block statement (curly braces). This creates a new scope for the declaration, preventing it from conflicting with other declarations. Here’s an example:

switch (condition) {
  case 'A': {
    let value = 1;
    console.log(value);
    break;
  }
  case 'B': {
    let value = 2;
    console.log(value);
    break;
  }
  default: {
    let value = 0;
    console.log(value);
    break;
  }
}

In this example, we wrap each case block in curly braces, creating a new scope for the value variable. This allows us to declare the variable within each block without causing conflicts.

These solutions should help you resolve the eslint: no-case-declaration error and ensure that your code follows best practices. Remember to always test your code after making changes to ensure it behaves as expected.

Happy coding!