Add overlay for build errors when using hmr (#1074)

src/builtins/hmr-runtime.js

@@ -1,3 +1,5 @@
+var OVERLAY_ID = '__parcel__error__overlay__';
+
 var global = (1, eval)('this');
 var OldModule = module.bundle.Module;
 
@@ -49,14 +51,51 @@ if ((!parent || !parent.isParcelRequire) && typeof WebSocket !== 'undefined') {
 
     if (data.type === 'error-resolved') {
       console.log('[parcel] ✨ Error resolved');
+
+      removeErrorOverlay();
     }
 
     if (data.type === 'error') {
       console.error('[parcel] 🚨  ' + data.error.message + '\n' + data.error.stack);
+
+      removeErrorOverlay();
+
+      var overlay = createErrorOverlay(data);
+      document.body.appendChild(overlay);
     }
   };
 }
 
+function removeErrorOverlay() {
+  var overlay = document.getElementById(OVERLAY_ID);
+  if (overlay) {
+    overlay.remove();
+  }
+}
+
+function createErrorOverlay(data) {
+  var overlay = document.createElement('div');
+  overlay.id = OVERLAY_ID;
+
+  // html encode message and stack trace
+  var message = document.createElement('div');
+  var stackTrace = document.createElement('pre');
+  message.innerText = data.error.message;
+  stackTrace.innerText = data.error.stack;
+
+  overlay.innerHTML = (
+    '<div style="background: black; font-size: 16px; color: white; position: fixed; height: 100%; width: 100%; top: 0px; left: 0px; padding: 30px; opacity: 0.85; font-family: Menlo, Consolas, monospace; z-index: 9999;">' +
+      '<span style="background: red; padding: 2px 4px; border-radius: 2px;">ERROR</span>' +
+      '<span style="top: 2px; margin-left: 5px; position: relative;">🚨</span>' +
+      '<div style="font-size: 18px; font-weight: bold; margin-top: 20px;">' + message.innerHTML + '</div>' +
+      '<pre>' + stackTrace.innerHTML + '</pre>' +
+    '</div>'
+  );
+
+  return overlay;
+
+}
+
 function getParents(bundle, id) {
   var modules = bundle.modules;
   if (!modules) {

test/hmr.js

@@ -7,6 +7,7 @@ const promisify = require('../src/utils/promisify');
 const ncp = promisify(require('ncp'));
 const WebSocket = require('ws');
 const json5 = require('json5');
+const sinon = require('sinon');
 
 describe('hmr', function() {
   let b, ws;
@@ -299,20 +300,26 @@ describe('hmr', function() {
     assert.deepEqual(outputs, [3, 10]);
   });
 
-  it('should log emitted errors', async function() {
+  it('should log emitted errors and show an error overlay', async function() {
     await ncp(__dirname + '/integration/commonjs', __dirname + '/input');
 
     b = bundler(__dirname + '/input/index.js', {watch: true, hmr: true});
     let bundle = await b.bundle();
 
     let logs = [];
-    run(bundle, {
-      console: {
-        error(msg) {
-          logs.push(msg);
+    let ctx = run(
+      bundle,
+      {
+        console: {
+          error(msg) {
+            logs.push(msg);
+          }
         }
-      }
-    });
+      },
+      {require: false}
+    );
+
+    let spy = sinon.spy(ctx.document.body, 'appendChild');
 
     fs.writeFileSync(
       __dirname + '/input/local.js',
@@ -323,6 +330,7 @@ describe('hmr', function() {
 
     assert.equal(logs.length, 1);
     assert(logs[0].trim().startsWith('[parcel] 🚨'));
+    assert(spy.calledOnce);
   });
 
   it('should log when errors resolve', async function() {
@@ -332,22 +340,32 @@ describe('hmr', function() {
     let bundle = await b.bundle();
 
     let logs = [];
-    run(bundle, {
-      console: {
-        error(msg) {
-          logs.push(msg);
-        },
-        log(msg) {
-          logs.push(msg);
+    let ctx = run(
+      bundle,
+      {
+        console: {
+          error(msg) {
+            logs.push(msg);
+          },
+          log(msg) {
+            logs.push(msg);
+          }
         }
-      }
-    });
+      },
+      {require: false}
+    );
+
+    let appendSpy = sinon.spy(ctx.document.body, 'appendChild');
+    let removeSpy = sinon.spy(ctx.document.getElementById('tmp'), 'remove');
 
     fs.writeFileSync(
       __dirname + '/input/local.js',
       'require("fs"; exports.a = 5; exports.b = 5;'
     );
     await nextEvent(b, 'buildEnd');
+    await sleep(50);
+
+    assert(appendSpy.called);
 
     fs.writeFileSync(
       __dirname + '/input/local.js',
@@ -356,6 +374,8 @@ describe('hmr', function() {
     await nextEvent(b, 'buildEnd');
     await sleep(50);
 
+    assert(removeSpy.called);
+
     assert.equal(logs.length, 2);
     assert(logs[0].trim().startsWith('[parcel] 🚨'));
     assert(logs[1].trim().startsWith('[parcel] ✨'));

test/utils.js

@@ -46,6 +46,10 @@ function bundle(file, opts) {
 
 function prepareBrowserContext(bundle, globals) {
   // for testing dynamic imports
+  const fakeElement = {
+    remove() {}
+  };
+
   const fakeDocument = {
     createElement(tag) {
       return {tag};
@@ -68,6 +72,16 @@ function prepareBrowserContext(bundle, globals) {
           }
         }
       ];
+    },
+
+    getElementById() {
+      return fakeElement;
+    },
+
+    body: {
+      appendChild() {
+        return null;
+      }
     }
   };