Skip to content

Transform async/await to somewhat idiomatic JavaScript promise chains

License

Notifications You must be signed in to change notification settings

rpetrich/babel-plugin-transform-async-to-promises

Folders and files

NameName
Last commit message
Last commit date

Latest commit

c7c006c · Dec 29, 2021
Dec 16, 2021
Dec 20, 2021
Dec 22, 2021
Dec 20, 2021
Aug 4, 2019
Aug 4, 2019
Dec 20, 2021
Dec 20, 2021
Dec 29, 2021
Dec 22, 2021
Apr 20, 2019
Dec 22, 2021
Dec 29, 2021
Dec 29, 2021
Aug 4, 2019

Repository files navigation

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:

async function fetchAsObjectURL(url) {
    const response = await fetch(url);
    const blob = await response.blob();
    return URL.createObjectURL(blob);
}

Output:

const fetchAsObjectURL = _async(function(url) {
	return _await(fetch(url), function(response) {
		return _await(response.blob(), URL.createObjectURL);
	});
});

Output with hoist enabled:

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:

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:

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

About

Transform async/await to somewhat idiomatic JavaScript promise chains

Resources

License

Stars

Watchers

Forks

Packages

No packages published