Attempt to load theme.js when rendering (#504)

Author: cpriest

src/lib/output/renderer.ts

@@ -201,7 +201,21 @@ export class Renderer extends ChildableComponent<Application, RendererComponent>
                 }
             }
 
-            this.theme = this.addComponent('theme', new DefaultTheme(this, path));
+            const filename = Path.join(path, 'theme.js');
+            if (!FS.existsSync(filename)) {
+                this.theme = this.addComponent('theme', new DefaultTheme(this, path));
+            } else {
+                try {
+                    const themeClass = typeof require(filename) === 'function' ? require(filename) : require(filename).default;
+
+                    this.theme = this.addComponent('theme', new (themeClass)(this, path));
+                } catch (err) {
+                    throw new Error(
+                        `Exception while loading "${filename}". You must export a \`new Theme(renderer, basePath)\` compatible class.\n` +
+                        err
+                    );
+                }
+            }
         }
 
         this.theme.resources.activate();