Switch Expression

[Lenmint]

🔍 Search Terms

Switch, Switch expression

✅ Viability Checklist

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
• This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

⭐ Suggestion

A switch expression like C# or any language.
So i can avoid using Immediately Invoked Function Expression

📃 Motivating Example

Instead of doing this

type State = 'loading' | 'success' | 'error';

const uiMessage = (() => {
  const state: State = 'success';

  switch (state) {
    case 'loading': return 'Fetching data...';
    case 'success': return 'Data loaded!';
    default:
      return 'Unknown error';
  }
})();

let's do this, like C#

type State = 'loading' | 'success' | 'error';

const uiMessage: string = state switch {
    'loading'  => 'Fetching data...',
    'success' => return 'Data loaded!',
    default => 'Unknown error',
}

### 💻 Use Cases

1. What do you want to use this for?
3. What shortcomings exist with current approaches?
4. What workarounds are you using in the meantime?

[MartinJohns]

This is out of scope for TypeScript. You mistakenly checked this part of the viability checklist:

This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)