Unneeded temporary introduced for named class expression with static property initializer

Search Terms

classes, static properties, temporary variable

Suggestion

When a class expression is returned from a function, it gets assigned to a temporary variable that is not needed there.

Use Cases

Less verbose and more clear JavaScript output.

Examples

Input:

const f = () => class   { static x = 1; };
const g = () => class _ { static x = 1; };
const h = () => { class _ { static x = 1; } return _; };

Current output (3.7.2) (formatted a little differently):

const f = () => { var _a; return _a = class { }, _a.x = 1, _a; };
const g = () => { var _a; return _a = class _ { }, _a.x = 1, _a; };
const h = () => { class _ { }; _.x = 1; return _; };

Desired output:

const f = () => { var _a = class { }; _a.x = 1; return _a; };
const g = () => { class _ { } _.x = 1; return _; };
const h = () => { class _ { } _.x = 1; return _; };

Checklist

My suggestion meets these guidelines:

• 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, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

Inizia riproducendo i tre esempi TypeScript e confrontando l’output JavaScript attuale con quello desiderato. Traccia come vengono emesse le espressioni di classe con nome e anonime con inizializzatori di proprietà statiche, quindi verifica che l’output generato eviti il temporaneo non necessario preservando il comportamento a runtime.