flow like the river

BACK_BACK/node_modules/parcel-bundler/lib/builtins/bundle-loader.js

@@ -0,0 +1,83 @@
+var getBundleURL = require('./bundle-url').getBundleURL;
+
+function loadBundlesLazy(bundles) {
+  if (!Array.isArray(bundles)) {
+    bundles = [bundles]
+  }
+
+  var id = bundles[bundles.length - 1];
+
+  try {
+    return Promise.resolve(require(id));
+  } catch (err) {
+    if (err.code === 'MODULE_NOT_FOUND') {
+      return new LazyPromise(function (resolve, reject) {
+        loadBundles(bundles.slice(0, -1))
+          .then(function () {
+            return require(id);
+          })
+          .then(resolve, reject);
+      });
+    }
+
+    throw err;
+  }
+}
+
+function loadBundles(bundles) {
+  return Promise.all(bundles.map(loadBundle));
+}
+
+var bundleLoaders = {};
+function registerBundleLoader(type, loader) {
+  bundleLoaders[type] = loader;
+}
+
+module.exports = exports = loadBundlesLazy;
+exports.load = loadBundles;
+exports.register = registerBundleLoader;
+
+var bundles = {};
+function loadBundle(bundle) {
+  var id;
+  if (Array.isArray(bundle)) {
+    id = bundle[1];
+    bundle = bundle[0];
+  }
+
+  if (bundles[bundle]) {
+    return bundles[bundle];
+  }
+
+  var type = (bundle.substring(bundle.lastIndexOf('.') + 1, bundle.length) || bundle).toLowerCase();
+  var bundleLoader = bundleLoaders[type];
+  if (bundleLoader) {
+    return bundles[bundle] = bundleLoader(getBundleURL() + bundle)
+      .then(function (resolved) {
+        if (resolved) {
+          module.bundle.register(id, resolved);
+        }
+
+        return resolved;
+      }).catch(function(e) {
+        delete bundles[bundle];
+        
+        throw e;
+      });
+  }
+}
+
+function LazyPromise(executor) {
+  this.executor = executor;
+  this.promise = null;
+}
+
+LazyPromise.prototype.then = function (onSuccess, onError) {
+  if (this.promise === null) this.promise = new Promise(this.executor)
+  return this.promise.then(onSuccess, onError)
+};
+
+LazyPromise.prototype.catch = function (onError) {
+  if (this.promise === null) this.promise = new Promise(this.executor)
+  return this.promise.catch(onError)
+};