Fix HMR failure with js error on load, take 2

packages/core/integration-tests/test/hmr.js

@@ -1,7 +1,8 @@
 const assert = require('assert');
 const fs = require('@parcel/fs');
 const path = require('path');
-const {bundler, run, rimraf, ncp} = require('@parcel/test-utils');
+const {bundler, run, rimraf, ncp, prepareBrowserContext} = require('@parcel/test-utils');
+const vm = require('vm');
 const {sleep} = require('@parcel/test-utils');
 const WebSocket = require('ws');
 const json5 = require('json5');
@@ -287,6 +288,52 @@ describe('hmr', function() {
     assert.deepEqual(outputs, [3, 10]);
   });
 
+  it('should accept HMR updates in the runtime after an initial error', async function() {
+    await fs.mkdirp(path.join(__dirname, '/input'));
+    fs.writeFile(
+      path.join(__dirname, '/input/index.js'),
+      'throw new Error("Something");\noutput(123);'
+    );
+
+    b = bundler(path.join(__dirname, '/input/index.js'), {
+      watch: true,
+      hmr: true
+    });
+    let bundle = await b.bundle();
+
+    let outputs = [];
+    let errors = [];
+
+    var ctx = prepareBrowserContext(bundle, {
+      output(o) {
+        outputs.push(o);
+      },
+      error(e) {
+        errors.push(e);
+      }
+    });
+    vm.createContext(ctx);
+    vm.runInContext(
+      `try {
+        ${(await fs.readFile(bundle.name)).toString()}
+      } catch(e) {
+        error(e);
+      }`,
+      ctx
+    );
+
+    assert.deepEqual(outputs, []);
+    assert.equal(errors.length, 1);
+    assert.equal(errors[0].message, 'Something');
+
+    await sleep(100);
+    fs.writeFile(path.join(__dirname, '/input/index.js'), 'output(123);');
+
+    await nextEvent(b, 'bundled');
+    assert.deepEqual(outputs, [123]);
+    assert.equal(errors.length, 1);
+  });
+
   it('should call dispose and accept callbacks', async function() {
     await ncp(
       path.join(__dirname, '/integration/hmr-callbacks'),

packages/core/parcel-bundler/src/builtins/prelude.js

@@ -77,8 +77,16 @@ parcelRequire = (function (modules, cache, entry, globalName) {
     }, {}];
   };
 
+  var error;
   for (var i = 0; i < entry.length; i++) {
-    newRequire(entry[i]);
+    try{
+      newRequire(entry[i]);
+    } catch(e){
+      // Save first error but execute all entries
+      if(!error){
+        error = e;
+      }
+    }
   }
 
   if (entry.length) {
@@ -103,5 +111,12 @@ parcelRequire = (function (modules, cache, entry, globalName) {
   }
 
   // Override the current require with this new one
+  parcelRequire = newRequire;
+
+  if(error){
+    // throw error from earlier, _after updating parcelRequire_
+    throw error;
+  }
+
   return newRequire;
 })

packages/core/test-utils/src/utils.js

@@ -289,6 +289,7 @@ exports.symlinkPrivilegeWarning = symlinkPrivilegeWarning;
 exports.bundler = bundler;
 exports.bundle = bundle;
 exports.run = run;
+exports.prepareBrowserContext = prepareBrowserContext;
 exports.assertBundleTree = assertBundleTree;
 exports.nextBundle = nextBundle;
 exports.deferred = deferred;