refactor: add emitter for code generation

src/render/render.ts

@@ -2,23 +2,24 @@ import { RenderError } from '../util/error'
 import assert from '../util/assert'
 import Context from '../context/context'
 import ITemplate from '../template/itemplate'
+import { Emitter } from './emitter'
 
 export default class Render {
   public async renderTemplates (templates: ITemplate[], ctx: Context) {
     assert(ctx, 'unable to evalTemplates: context undefined')
 
-    let html = ''
+    const emitter = new Emitter()
     for (const tpl of templates) {
       try {
-        html += await tpl.render(ctx)
+        emitter.write(await tpl.render(ctx, emitter))
       } catch (e) {
         if (e.name === 'RenderBreakError') {
-          e.resolvedHTML = html
+          e.resolvedHTML = emitter.html
           throw e
         }
         throw e.name === 'RenderError' ? e : new RenderError(e, tpl)
       }
     }
-    return html
+    return emitter.html
   }
 }