ambi/edition-browsers/index.js

Ambi lets you execute any function ambidextrously; providing you the ability to execute any function (be it synchronous, asynchronous, returns, callbacks, promises) as if it returned a promise.

// Import
import { isError } from 'typechecker';
// Handle success case
function onSuccess(value) {
    // Reject if an error was returned
    if (isError(value))
        return Promise.reject(value);
    // Success case, so return the value
    return value;
}
/**
 * Ambidextrously execute the method with the passed arguments.
 * If method.length > args.length, then ambi provides the method with a completion callback as the last expected argument.
 * @param method A method, that can either resolve synchronously, via a promise, or via a callback.
 * @param args The arguments to provide the function.
 * @returns The determined result.
 */
export default function ambi(method, ...args) {
    /*
    Different ways functions can be called:
    ambi(function(a,next){next(null, a)}, a)
        > method.length > args.length
        > next will be provided automatically
    ambi(function(a){return a}, a)
        > method.length = args.length
        > no argument changes by ambi
    ambi(function(a){return a}, a, b)
        > method.length < args.length
        > no argument changes by ambi
    */
    try {
        // Inject a completion callback
        if (method.length > args.length) {
            return new Promise(function (resolve, reject) {
                const xargs = args
                    .slice()
                    // add the difference as undefined values
                    .concat(new Array(method.length - args.length - 1))
                    // add the completion callback
                    .concat([
                    function ambiCallback(err, ...args) {
                        if (err)
                            return reject(err);
                        if (args.length === 1)
                            return resolve(args[0]);
                        return resolve(args);
                    },
                ]);
                method(...xargs);
            }).then(onSuccess);
        }
        // Execute without a completion callback
        else {
            return Promise.resolve(method(...args)).then(onSuccess);
        }
    }
    catch (err) {
        return Promise.reject(err);
    }
}