Migration from Angular 6 to Angular 7 cause error - Can't resolve 'core-js/es7/reflect'

Question

Global Angular CLI: 7.3.8
Node v10.15.3
NPM 6.4.1
macos

I'm getting this error on npm start

ERROR in ./node_modules/@angular-devkit/build-angular/src/angular-cli-files/models/jit-polyfills.js Module not found: Error: Can't resolve 'core-js/es7/reflect' in '/Users/XXX/projects/XXX/node_modules/@angular-devkit/build-angular/src/angular-cli-files/models' ERROR in ./src/polyfills.ts Module not found: Error: Can't resolve 'core-js/es7/reflect' in '/Users/XXX/projects/XXX/src'

For projects being upgraded to Angular 8 or later, you can uninstall core.js as a dependency: https://stackoverflow.com/questions/56892243/is-not-core-js-needed-anymore — John Gilmer, Oct 23 '20 at 07:18
@JohnGilmer Thank you for your comment. Feel free to add it as an answer. It will be helpful — Dmitry Grinko, Oct 23 '20 at 19:35

score 18 · Accepted Answer · answered Apr 18 '19 at 19:41

To solve this issue I've added the following paths to compilerOptions in tsconfig.json

{
  "compileOnSave": false,
  "compilerOptions": {
    "paths": {
      "core-js/es7/reflect": [
        "node_modules/core-js/proposals/reflect-metadata",
      ],
      "core-js/es6/*": ["node_modules/core-js/es"]
    },
    "baseUrl": "./",
    "outDir": "./dist/out-tsc",
    "sourceMap": true,
    "declaration": false,
    "moduleResolution": "node",
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "target": "es5",
    "typeRoots": [
      "node_modules/@types"
    ],
    "lib": [
      "es2017",
      "dom"
    ]
  }
}

you're a life saver. This is what was needed for me as well. — 今際のアリス, May 17 '19 at 18:47

score 5 · Answer 2 · answered Jul 18 '19 at 12:36

5

After Migrated to new Angular version, 'core-js/es6' or 'core-js/es7' Will not work.

You have to simply replace import 'core-js/es/'

For ex. import 'core-js/es6/symbol' to import 'core-js/es/symbol'

This will work properly.

answered Jul 18 '19 at 12:36

Bhadresh Patel

1,671
17
18

score 2 · Answer 3 · answered Jan 16 '20 at 14:11

2

just remove the number at the end of 'es' in the path, like 'core-js/es/reflect'. It worked for me.

answered Jan 16 '20 at 14:11

Stanley Mohlala

6,816
1
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score 0 · Answer 4 · answered Nov 12 '19 at 09:05

0

I just copy all from my oldest project src/polyfills to the new imported. That's help ;) .

answered Nov 12 '19 at 09:05

Sergiu Siscovschi

1
1

score 0 · Answer 5 · edited Oct 09 '20 at 13:15

0

Getting this error in "@angular/cli": "~10.1.5" project:

Cannot find module 'core-js/es7/reflect' or its corresponding type declarations.ts(2307)

Solution:

import * as Reflect from 'core-js/es';

edited Oct 09 '20 at 13:15

fcdt

2,371
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answered Oct 09 '20 at 11:34

Pinaki

792
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Migration from Angular 6 to Angular 7 cause error - Can't resolve 'core-js/es7/reflect'

5 Answers5