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https://github.com/rpetrich/babel-plugin-transform-async-to-promises
Transform async/await to somewhat idiomatic JavaScript promise chains
https://github.com/rpetrich/babel-plugin-transform-async-to-promises
Last synced: about 1 month ago
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Transform async/await to somewhat idiomatic JavaScript promise chains
- Host: GitHub
- URL: https://github.com/rpetrich/babel-plugin-transform-async-to-promises
- Owner: rpetrich
- License: mit
- Created: 2018-01-06T23:27:25.000Z (almost 7 years ago)
- Default Branch: master
- Last Pushed: 2023-03-04T02:31:27.000Z (almost 2 years ago)
- Last Synced: 2024-09-08T13:45:05.679Z (4 months ago)
- Language: TypeScript
- Homepage:
- Size: 2.35 MB
- Stars: 246
- Watchers: 6
- Forks: 17
- Open Issues: 15
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
babel-plugin-transform-async-to-promises
========================================
Babel plugin to transform `async` functions containing `await` expressions to the equivalent chain of `Promise` calls with use of minimal helper functions.
### Input:
```javascript
async function fetchAsObjectURL(url) {
const response = await fetch(url);
const blob = await response.blob();
return URL.createObjectURL(blob);
}
```
### Output:
```javascript
const fetchAsObjectURL = _async(function(url) {
return _await(fetch(url), function(response) {
return _await(response.blob(), URL.createObjectURL);
});
});
```
### Output with `hoist` enabled:
```javascript
function _response$blob(response) {
return _await(response.blob(), URL.createObjectURL);
}
const fetchAsObjectURL = _async(function(url) {
return _await(fetch(url), _response$blob);
});
```
### Output with `inlineHelpers` enabled:
```javascript
const fetchAsObjectURL = function(url) {
try {
return Promise.resolve(fetch(url)).then(function(response) {
return Promise.resolve(response.blob()).then(URL.createObjectURL);
});
} catch(e) {
return Promise.reject(e);
}
}
```
### Output with `externalHelpers` enabled:
In the normal case, helpers are added to the top of the file for the `_async` and `_await` functions (as well as others). This can cause bloat in a codebase due to duplication of helper code in every file. To avoid this, enable `externalHelpers` and those will be imported instead:
```javascript
import { _async } from "babel-plugin-transform-async-to-promises/helpers";
import { _await } from "babel-plugin-transform-async-to-promises/helpers";
const fetchAsObjectURL = _async(function(url) {
return _await(fetch(url), function(response) {
return _await(response.blob(), URL.createObjectURL);
});
});
export default fetchAsObjectURL;
```
## JavaScript Language Features
### Full Support
- `async`/`await`
- `for`/`while`/`do` loops (including loops that would exhaust stack if dispatched recursively)
- `switch` statements (including fallthrough and `default` cases)
- conditional expressions
- logical expressions
- `try`/`catch`
- `break`/`continue` statements (on both loops and labeled statements)
- `throw` expressions
- Function hoisting
- Variable hoisting
- Arrow functions
- Methods
- `arguments`
- `this`
- Proper member dereference order of operations
- Standards-compliant event loop scheduling
### Partial Support
- `Function.length`: `async` functions will often return a length of 0 (when the `_async` wrapper is used)
- Top level await support is experimental with compatible module bundler. Set `topLevelAwait` option to `return` when using SystemJS.
### No support
- `eval`: impossible to support without deep hooks into the runtime
- Async generator functions: not implemented or planned
- `Function.name`: rewrite pass removes function name instrumentation
- `new AsyncFunction(...)`: impossible to support without shipping babel and the plugin in the output