Require/AMD and async resources in 2015 - asynchronous

Question

I'm building a library which uses asynchronous resources. I want the library to be loadable with AMD/require.
I've seen this discussion from 2011 about promises support, but it went nowhere.
I've seen plugins like async and require-promise - but I don't know how I feel about a library installing plugins.
I'm interested to know if anything has changed in terms of loading resources and/or dependent scripts. If promises are not supported, is there another way to signal requirejs that a script is ready in an asynchronous way?

Answer 1

I dived into the source of require.js, and I didn't find a way to make an asynchronous define. Plugins have the capability, but simple defines do not. I think the reason behind this is that async circular dependencies are a bit tricky.
However it is not impossible to write a mini async require-like library:
(function(context) {
const modules = new Map();
function require(name) {
return Promise.resolve(null).then(function() {
const module = modules.get(name);
if (!module) throw new Error("Undefined module");
if (module.promise) {
return module.exports;
} else {
return module.promise = Promise.all(
module.deps.map(internalRequire)
).then(function(args) {
return module.factory.apply(context, args);
}).then(function(defExport) {
if (defExport !== undefined) {
module.exports.default = defExport;
}
return module.exports;
});
}
function internalRequire(name) {
return (name === 'exports') ? module.exports : require(name);
}
});
}
function define(name, deps, factory) {
if (modules.has(name)) throw new Error("Redefined module");
modules.set(name, {
name: name,
deps: deps,
factory: factory,
exports: {},
promise: null
});
}
context.require = require;
context.define = define;
})(self);
Usage:
define('A', ['B'], function(dep) {
return new Promise(function(resolve) {
setTimeout(function() {
resolve("A(" + dep.default + ")");
}, 100);
});
});
define('B', ['C'], function(dep) {
return new Promise(function(resolve) {
setTimeout(function() {
resolve("B(" + dep.default + ")");
}, 100);
});
});
define('C', ['A'], function(dep) {
return new Promise(function(resolve) {
setTimeout(function() {
resolve("C(" + dep.default + ")");
}, 100);
});
});
require("A").then(function(s) {
console.log(s);
});