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);
}
}
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)
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 instrumentationnew AsyncFunction(...)
: impossible to support without shipping babel and the plugin in the output