Expose all built-in options for getConstructor

Quoting #264 (comment)

> Regarding `Encountered error "#<ExecJS::ProgramError: Invariant
> Violation: Element type is invalid: ...`:
>
> I think one of the core issues is that [module lookup uses
> `try...catch`](https://github.com/reactjs/react-rails/blob/master/react_ujs/src/getConstructor/fromRequireContextWithGlobalFallback.js#L11-L23).
> While the errors are logged to the console shim, that typically doesn't
> help as a later error (such as the invariant violation) will lead to a
> fatal error (triggering a 500). If that could be refactored to be a bit
> more intentional based on environment (instead of just reacting based on
> exceptions, or at the very least, throwing if the caught exception isn't
> very specific)

This enables us to easily override `getConstructor` to not use global
fallback, avoiding the all-consuming `try...catch`.

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 #### New Features
 
+- Expose alternative implementations for `ReactUJS.getConstructor` #1050
+
 #### Deprecation
 
 #### Bug Fixes

README.md

@@ -406,13 +406,27 @@ delete window.Turbolinks;
 
 ### `getConstructor`
 
-Components are loaded with `ReactRailsUJS.getConstructor(className)`. This function has two built-in implementations:
+Components are loaded with `ReactRailsUJS.getConstructor(className)`. This function has two default implementations, depending on if you're using the asset pipeline or Webpacker:
 
-- On the asset pipeline, it looks up `className` in the global namespace.
-- On Webpacker, it `require`s files and accesses named exports, as described in [Get started with Webpacker](#get-started-with-webpacker).
+- On the asset pipeline, it looks up `className` in the global namespace (`ReactUJS.constructorFromGlobal`).
+- On Webpacker, it `require`s files and accesses named exports, as described in [Get started with Webpacker](#get-started-with-webpacker), falling back to the global namespace (`ReactUJS.constructorFromRequireContextWithGlobalFallback`).
 
 You can override this function to customize the mapping of name-to-constructor. [Server-side rendering](#server-side-rendering) also uses this function.
 
+For example, the fallback behavior of
+`ReactUJS.constructorFromRequireContextWithGlobalFallback` can sometimes make
+server-side rendering errors hard to debug as it will swallow the original error
+(more info
+[here](https://github.com/reactjs/react-rails/issues/264#issuecomment-552326663)).
+`ReactUJS.constructorFromRequireContext` is provided for this reason. You can
+use it like so:
+
+```js
+// Replaces calls to `ReactUJS.useContext`
+ReactUJS.getConstructor = ReactUJS.constructorFromRequireContext(require.context('components', true));
+```
+
+
 ## Server-Side Rendering
 
 You can render React components inside your Rails server with `prerender: true`:

lib/assets/javascripts/react_ujs.js

@@ -7,7 +7,7 @@
 		exports["ReactRailsUJS"] = factory(require("react-dom"), require("react"), require("react-dom/server"));
 	else
 		root["ReactRailsUJS"] = factory(root["ReactDOM"], root["React"], root["ReactDOMServer"]);
-})(this, function(__WEBPACK_EXTERNAL_MODULE_1__, __WEBPACK_EXTERNAL_MODULE_5__, __WEBPACK_EXTERNAL_MODULE_6__) {
+})(this, function(__WEBPACK_EXTERNAL_MODULE_2__, __WEBPACK_EXTERNAL_MODULE_6__, __WEBPACK_EXTERNAL_MODULE_7__) {
 return /******/ (function(modules) { // webpackBootstrap
 /******/ 	// The module cache
 /******/ 	var installedModules = {};
@@ -73,7 +73,7 @@ return /******/ (function(modules) { // webpackBootstrap
 /******/ 	__webpack_require__.p = "";
 /******/
 /******/ 	// Load entry module and return exports
-/******/ 	return __webpack_require__(__webpack_require__.s = 7);
+/******/ 	return __webpack_require__(__webpack_require__.s = 8);
 /******/ })
 /************************************************************************/
 /******/ ([
@@ -108,17 +108,47 @@ module.exports = function(className) {
 /* 1 */
 /***/ (function(module, exports) {
 
-module.exports = __WEBPACK_EXTERNAL_MODULE_1__;
+// Load React components by requiring them from "components/", for example:
+//
+// - "pages/index" -> `require("components/pages/index")`
+// - "pages/show.Header" -> `require("components/pages/show").Header`
+// - "pages/show.Body.Content" -> `require("components/pages/show").Body.Content`
+//
+module.exports = function(reqctx) {
+  return function(className) {
+    var parts = className.split(".")
+    var filename = parts.shift()
+    var keys = parts
+    // Load the module:
+    var component = reqctx("./" + filename)
+    // Then access each key:
+    keys.forEach(function(k) {
+      component = component[k]
+    })
+    // support `export default`
+    if (component.__esModule) {
+      component = component["default"]
+    }
+    return component
+  }
+}
+
 
 /***/ }),
 /* 2 */
+/***/ (function(module, exports) {
+
+module.exports = __WEBPACK_EXTERNAL_MODULE_2__;
+
+/***/ }),
+/* 3 */
 /***/ (function(module, exports, __webpack_require__) {
 
-var nativeEvents = __webpack_require__(8)
-var pjaxEvents = __webpack_require__(9)
-var turbolinksEvents = __webpack_require__(10)
-var turbolinksClassicDeprecatedEvents = __webpack_require__(12)
-var turbolinksClassicEvents = __webpack_require__(11)
+var nativeEvents = __webpack_require__(9)
+var pjaxEvents = __webpack_require__(10)
+var turbolinksEvents = __webpack_require__(11)
+var turbolinksClassicDeprecatedEvents = __webpack_require__(13)
+var turbolinksClassicEvents = __webpack_require__(12)
 
 // see what things are globally available
 // and setup event handlers to those things
@@ -170,14 +200,14 @@ module.exports = function(ujs) {
 
 
 /***/ }),
-/* 3 */
+/* 4 */
 /***/ (function(module, exports, __webpack_require__) {
 
 // Make a function which:
 // - First tries to require the name
 // - Then falls back to global lookup
 var fromGlobal = __webpack_require__(0)
-var fromRequireContext = __webpack_require__(13)
+var fromRequireContext = __webpack_require__(1)
 
 module.exports = function(reqctx) {
   var fromCtx = fromRequireContext(reqctx)
@@ -201,15 +231,15 @@ module.exports = function(reqctx) {
 
 
 /***/ }),
-/* 4 */
+/* 5 */
 /***/ (function(module, __webpack_exports__, __webpack_require__) {
 
 "use strict";
 Object.defineProperty(__webpack_exports__, "__esModule", { value: true });
 /* harmony export (immutable) */ __webpack_exports__["supportsHydration"] = supportsHydration;
 /* harmony export (immutable) */ __webpack_exports__["reactHydrate"] = reactHydrate;
 /* harmony export (immutable) */ __webpack_exports__["createReactRootLike"] = createReactRootLike;
-const ReactDOM = __webpack_require__(1)
+const ReactDOM = __webpack_require__(2)
 
 function supportsHydration() {
   return typeof ReactDOM.hydrate === "function" || typeof ReactDOM.hydrateRoot === "function"
@@ -238,29 +268,30 @@ function legacyReactRootLike(node) {
 
 
 /***/ }),
-/* 5 */
+/* 6 */
 /***/ (function(module, exports) {
 
-module.exports = __WEBPACK_EXTERNAL_MODULE_5__;
+module.exports = __WEBPACK_EXTERNAL_MODULE_6__;
 
 /***/ }),
-/* 6 */
+/* 7 */
 /***/ (function(module, exports) {
 
-module.exports = __WEBPACK_EXTERNAL_MODULE_6__;
+module.exports = __WEBPACK_EXTERNAL_MODULE_7__;
 
 /***/ }),
-/* 7 */
+/* 8 */
 /***/ (function(module, exports, __webpack_require__) {
 
-var React = __webpack_require__(5)
-var ReactDOM = __webpack_require__(1)
-var ReactDOMServer = __webpack_require__(6)
+var React = __webpack_require__(6)
+var ReactDOM = __webpack_require__(2)
+var ReactDOMServer = __webpack_require__(7)
 
-var detectEvents = __webpack_require__(2)
+var detectEvents = __webpack_require__(3)
 var constructorFromGlobal = __webpack_require__(0)
-var constructorFromRequireContextWithGlobalFallback = __webpack_require__(3)
-const { supportsHydration, reactHydrate, createReactRootLike } = __webpack_require__(4)
+var constructorFromRequireContext = __webpack_require__(1)
+var constructorFromRequireContextWithGlobalFallback = __webpack_require__(4)
+const { supportsHydration, reactHydrate, createReactRootLike } = __webpack_require__(5)
 
 var ReactRailsUJS = {
   // This attribute holds the name of component which should be mounted
@@ -321,6 +352,11 @@ var ReactRailsUJS = {
   // the default is ReactRailsUJS.ComponentGlobal
   getConstructor: constructorFromGlobal,
 
+  // Available for customizing `getConstructor`
+  constructorFromGlobal: constructorFromGlobal,
+  constructorFromRequireContext: constructorFromRequireContext,
+  constructorFromRequireContextWithGlobalFallback: constructorFromRequireContextWithGlobalFallback,
+
   // Given a Webpack `require.context`,
   // try finding components with `require`,
   // then falling back to global lookup.
@@ -395,6 +431,7 @@ var ReactRailsUJS = {
   detectEvents: function() {
     detectEvents(this)
   },
+
 }
 
 // These stable references are so that handlers can be added and removed:
@@ -429,7 +466,7 @@ module.exports = ReactRailsUJS
 
 
 /***/ }),
-/* 8 */
+/* 9 */
 /***/ (function(module, exports) {
 
 module.exports = {
@@ -452,7 +489,7 @@ module.exports = {
 
 
 /***/ }),
-/* 9 */
+/* 10 */
 /***/ (function(module, exports) {
 
 module.exports = {
@@ -472,7 +509,7 @@ module.exports = {
 
 
 /***/ }),
-/* 10 */
+/* 11 */
 /***/ (function(module, exports) {
 
 module.exports = {
@@ -488,7 +525,7 @@ module.exports = {
 
 
 /***/ }),
-/* 11 */
+/* 12 */
 /***/ (function(module, exports) {
 
 module.exports = {
@@ -506,7 +543,7 @@ module.exports = {
 
 
 /***/ }),
-/* 12 */
+/* 13 */
 /***/ (function(module, exports) {
 
 module.exports = {
@@ -526,36 +563,6 @@ module.exports = {
 }
 
 
-/***/ }),
-/* 13 */
-/***/ (function(module, exports) {
-
-// Load React components by requiring them from "components/", for example:
-//
-// - "pages/index" -> `require("components/pages/index")`
-// - "pages/show.Header" -> `require("components/pages/show").Header`
-// - "pages/show.Body.Content" -> `require("components/pages/show").Body.Content`
-//
-module.exports = function(reqctx) {
-  return function(className) {
-    var parts = className.split(".")
-    var filename = parts.shift()
-    var keys = parts
-    // Load the module:
-    var component = reqctx("./" + filename)
-    // Then access each key:
-    keys.forEach(function(k) {
-      component = component[k]
-    })
-    // support `export default`
-    if (component.__esModule) {
-      component = component["default"]
-    }
-    return component
-  }
-}
-
-
 /***/ })
 /******/ ]);
 });