A small helper function to bridge the gap when returning a promise from a function that takes a callback
Note that this module will not introduce any custom Promise implementation.
It will use the global Promise (requires node >= v4).
import withCallback from 'with-callback';
// or const withCallback = require('with-callback');
// withCallback returns a promise and invokes the function with a callback
// used to fulfill the promise
function readFile(name) {
return withCallback(callback => fs.readFile(name, callback));
}
// arguments can also be passed as an array
function readFile(name) {
return withCallback([name], fs.readFile);
}
// A second function can be passed to withCallback to map all arguments
// passed to the callback to a single value used to resolve the promise.
function example(callback) {
callback(null, 'a', 'b');
}
const promise = withCallback(example, (a, b) => [a, b]);
// promise resolves with ['a', 'b']