microsoft / microsoft/TypeScript

Shouldn't TypeScript be able to polyfill `import defer` with `Proxy` to work with `"module": "commonjs"`?

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#62,031 1 comment 0 reactions 0 assignees View on GitHub
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Description

### 🔍 Search Terms

import defer commonjs
import defer require

### ✅ Viability Checklist

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

### ⭐ Suggestion

Since the TypeScript beta announcement, I tried it in the playground. But setting `"module"` to `"commonjs"` sadly revealed that `import defer` only work with `"module": "esnext"` or `"module": "preserve"`.

But `Proxy` can polyfill this exact behavior.

### 📃 Motivating Example

This code:

```typescript
import defer * as MyModule from 'my-module'
```

should output something like this:

```javascript
let _module
const MyModule = new Proxy({}, {
get(_target, prop) {
if (!_module) {
_module = require('my-module') // the real code would obviously more complicated as it needs to force `_module` to be an object
}
return _module[prop]
}
})
```

### 💻 Use Cases

1. What do you want to use this for? Using `import defer` for legacy targets
2. What shortcomings exist with current approaches? `await import` forces `Promise`
3. What workarounds are you using in the meantime? `await import`

Contributor guide

Open the contributing guide

Research direction

Start by tracing how TypeScript handles `import defer` when `module` is `commonjs`, and compare that with the existing `esnext` and `preserve` behavior. Use the motivating `Proxy` example and the stated legacy-target use case to define the expected output, then add coverage showing whether synchronous deferred access works without introducing `Promise`.

Written by the indexing model from the issue text.

Assessment

Tech stack
javascript, typescript
Domain
compilers
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
28/100

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