use web component to show build progress; use Promise.all so errors are shown

app.js

@@ -40,15 +40,7 @@ import {lintKeymap} from '@codemirror/lint'
   ])
 ])()`
 
-function log(message, cls = 'cyan') {
-  const el = document.createElement('pre')
-  el.classList.add(cls)
-  el.innerText = message
-  document.body.append(el)
-  ;(el.scrollIntoViewIfNeeded ?? el.scrollIntoView).call(el)
-}
-
-class App {
+class Builder {
   jApiBaseUrl = 'https://data.jsdelivr.com/v1/'
   jCdnBaseUrl = 'https://cdn.jsdelivr.net/npm/'
 
@@ -73,9 +65,6 @@ class App {
 
   constructor() {
     this.downloads = []
-    this.run().catch(e => {
-      log(`${e}`)
-    })
   }
 
   checkOk(resp) {
@@ -104,7 +93,7 @@ class App {
       `${dep}@${version}/package.json`
     )
     this.checkOk(pkgResp)
-    log(dep)
+    this.log(dep)
     const pkg = await pkgResp.json()
     this.scripts[dep].path = (
       pkg.module ?? pkg.main
@@ -118,18 +107,22 @@ class App {
     )))
   }
 
-  async checkIntegrity(resp, name, script) {
-    const blob = await resp.blob()
-    const ab = await blob.arrayBuffer()
+  async sha(ab) {
     const hash = await crypto.subtle.digest(
       "SHA-256", ab
     )
-    const checkValue = 'sha256-' + btoa(
+    return 'sha256-' + btoa(
       String.fromCharCode(
         ...new Uint8Array(hash)
       )
     )
-    if (checkValue !== script.sha) {
+  }
+
+  async checkIntegrity(resp, name, script) {
+    const blob = await resp.blob()
+    const ab = await blob.arrayBuffer()
+    const sha = await this.sha(ab)
+    if (sha !== script.sha) {
       throw new Error(
         'failed integrity check: ' +
         `${checkValue} !== ${script.sha}`
@@ -139,7 +132,7 @@ class App {
   }
 
   async getScript(name) {
-    log('[downloading] ' + name, 'green')
+    this.log('[downloading] ' + name, 'green')
     const script = this.scripts[name]
     if (script.text) {
       return script.text
@@ -159,7 +152,10 @@ class App {
       script.text = await resp.text()
       script.sha = resp.integrity
     }
-    log('[downloaded] ' + url + ` [${script.text.length}]`, 'green')
+    this.log(
+      '[downloaded] ' + url + ` [${script.text.length}]`,
+      'green'
+    )
     return script.text
   }
 
@@ -180,29 +176,105 @@ class App {
       },
       load: async id => {
         if (id === 'editor.js') {
+          this.log(`[found] editor.js`)
           return editorSrc
         } else if (id in this.scripts) {
-          log(`[found] ${id}`)
+          this.log(`[found] ${id}`)
           return this.scripts[id].text
         }
       },
     }
   }
 
-  async run() {
-    await Promise.allSettled(
+  async build() {
+    const result = await Promise.all(
       this.topLevelDeps.map(dep => (
         this.loadDep(dep)
       ))
     )
-    await Promise.allSettled(this.downloads)
+    await Promise.all(this.downloads)
     await this.loadScript('@rollup/browser')
     const { rollup } = window.rollup
     const input = 'editor.js'
     const plugins = [this.loaderPlugin]
     const bundle = await rollup({input, plugins})
     const {output} = await bundle.generate({format: 'es'})
-    log(output[0].code)
+    this.code = output[0].code
+    this.sha = await this.sha(
+      new TextEncoder().encode(this.code)
+    )
+    this.log(`built ${this.sha}`)
+  }
+}
+
+class BuildView extends HTMLElement {
+  constructor() {
+    super()
+    this.attachShadow({mode: 'open'})
+    this.shadowRoot.adoptedStyleSheets = [
+      this.constructor.styleSheet
+    ]
+  }
+
+  log(message, cls = 'cyan') {
+    const el = document.createElement('pre')
+    el.classList.add(cls)
+    el.innerText = message
+    this.shadowRoot.append(el)
+    ;(el.scrollIntoViewIfNeeded ?? el.scrollIntoView).call(el)
+  }
+
+  static get styleSheet() {
+    if (this._styleSheet === undefined) {
+      this._styleSheet = new CSSStyleSheet()
+      this._styleSheet.replaceSync(this.css)
+    }
+    return this._styleSheet
+  }
+
+  static css = `
+    :host {
+      display: flex;
+      flex-direction: column;
+      align-items: stretch;
+      margin: 10px;
+      gap: 10px;
+    }
+
+    pre {
+      padding: 8px;
+      border-radius: 5px;
+      margin: 0;
+      overflow-x: auto;
+    }
+
+    pre.cyan {
+      background: cyan;
+    }
+
+    pre.green {
+      background: lightgreen;
+    }
+  `
+}
+
+customElements.define('m-build-view', BuildView)
+
+class App {
+  constructor() {
+    this.builder = new Builder()
+    this.buildView = document.createElement('m-build-view')
+    document.body.append(this.buildView)
+    this.builder.log = this.buildView.log.bind(this.buildView)
+    this.build()
+  }
+
+  async build() {
+    try {
+      await this.builder.build()
+    } catch (e) {
+      this.buildView.log(`${e}`)
+    }
   }
 }
 

style.css

@@ -9,21 +9,4 @@ body {
   padding: 0;
   margin: 0;
   background: navy;
-  margin: 10px;
-  gap: 10px;
-}
-
-pre {
-  padding: 8px;
-  border-radius: 5px;
-  margin: 0;
-  overflow-x: auto;
-}
-
-pre.cyan {
- background: cyan;
-}
-
-pre.green {
-  background: lightgreen;
 }