babel-plugin-transform-async-to-promises

What is babel-plugin-transform-async-to-promises?

The babel-plugin-transform-async-to-promises package is a Babel plugin that transforms async/await syntax into Promises, allowing for more efficient and compatible asynchronous code execution in environments that do not support async/await natively.

What are babel-plugin-transform-async-to-promises's main functionalities?

Transform async functions to Promises

This feature allows you to write asynchronous code using async/await syntax, which the plugin then transforms into Promise-based code for better compatibility and performance.

const example = async () => {
  const result = await someAsyncFunction();
  return result;
};

Optimize async/await code

The plugin optimizes the transformed code to reduce the overhead associated with async/await, making the resulting Promise-based code more efficient.

const example = async () => {
  const result1 = await someAsyncFunction1();
  const result2 = await someAsyncFunction2();
  return [result1, result2];
};

Other packages similar to babel-plugin-transform-async-to-promises

babel-plugin-transform-async-to-generator

This package transforms async/await syntax into generator functions. While it also aims to provide compatibility for environments that do not support async/await, it uses generator functions instead of Promises, which can result in different performance characteristics and code structure.

babel-plugin-syntax-async-functions

This package allows Babel to parse async functions but does not transform them. It is useful if you want to use async/await syntax in your code but rely on another tool or runtime to handle the actual transformation or execution.

babel-plugin-transform-regenerator

This package transforms generator functions and async functions to use regenerator runtime. It provides a broader transformation capability, including both async/await and generator functions, but may introduce additional runtime dependencies.

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:

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