Error: Can't resolve 'core-js/es7/reflect' in '\node_modules\@angular-devkit\build-angular\src\angular-cli-files\models

Question

After updating to Angular 7.3.6, I get the following error on ng serve:

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 '\node_modules@angular-devkit\build-angular\src\angular-cli-files\models'

Here is my package.json dependecies:

{
  "name": "frontend",
  "version": "0.0.0",
  "license": "MIT",
  "scripts": {
    "ng": "ng",
    "start": "ng serve",
    "build": "ng build --prod",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e"
  },
  "private": true,
  "dependencies": {
    "@angular/animations": "^7.2.11",
    "@angular/cdk": "^7.3.6",
    "@angular/common": "^7.2.11",
    "@angular/compiler": "^7.2.11",
    "@angular/core": "^7.2.11",
    "@angular/flex-layout": "^7.0.0-beta.24",
    "@angular/forms": "^7.2.11",
    "@angular/http": "^7.2.11",
    "@angular/material": "^7.3.6",
    "@angular/platform-browser": "^7.2.11",
    "@angular/platform-browser-dynamic": "^7.2.11",
    "@angular/router": "^7.2.11",
    "adm-zip": "^0.4.13",
    "core-js": "^2.6.5",
    "hammerjs": "^2.0.8",
    "rxjs": "^6.4.0",
    "rxjs-compat": "^6.0.0-rc.0",
    "tslib": "^1.9.3",
    "zone.js": "^0.9.0"
  },
  "devDependencies": {
    "@angular-devkit/build-angular": "^0.13.7",
    "@angular/cli": "^7.3.7",
    "@angular/compiler-cli": "^7.2.11",
    "@angular/language-service": "^7.2.11",
    "@types/jasmine": "~3.3.12",
    "@types/jasminewd2": "~2.0.6",
    "@types/node": "~11.12.0",
    "codelyzer": "^5.0.0",
    "jasmine-core": "~3.3.0",
    "jasmine-spec-reporter": "~4.2.1",
    "karma": "^4.0.1",
    "karma-chrome-launcher": "~2.2.0",
    "karma-coverage-istanbul-reporter": "^2.0.5",
    "karma-jasmine": "~2.0.1",
    "karma-jasmine-html-reporter": "^1.4.0",
    "protractor": "^6.0.0",
    "ts-node": "~8.0.3",
    "tslint": "~5.14.0",
    "typescript": "3.1.6"
  }
}

Windblown

Did you clean your node_modules, node cache and try npm install from fresh before running ng serve? – Attila

yes I did, but the same error keeps on appearing and I don't know what else to do. Do you have any other suggestions? – Windblown

You should install [email protected] – Attila

yes it worked! thank you – Windblown

Adding it as answer, please accept. – Attila

Did face the same issue! but thanks to @nircraft, it worked for me too. – Freshet

In core-js@3 es7 path removed. Use, for example, core-js/proposals/reflect-metadata. Here is the github link link – Thermometry

As of July 3, 2019, using Angular-CLI 8.0.6 and Angular 8.1.0, the above error will no longer happen on NEWLY GENERATED Angular apps because the offending import is no longer generated in /src/polyfills.ts. For older Angular applications, I suggest generating a temporary Angular app via: ``` ng new aaTemplate --skip-tests --skip-install ``` Compare the newly generated aaTemplate\src\polyfills.ts with your older application's polyfills.ts and you'll see what I'm talking about. – Isador

For projects being upgraded to Angular 8 or later, you can uninstall core.js as a dependency: #56892743 – Wolfe

Answer 1

You should install [email protected] that contains this file/module. See preset-env docs.

Also note, however, that this is a very old version with known issues and is unsupported. From the module itself:

"core-js@<3.23.3 is no longer maintained and not recommended for usage due to the number of issues. Because of the V8 engine whims, feature detection in old core-js versions could cause a slowdown up to 100x even if nothing is polyfilled. Some versions have web compatibility issues. Please, upgrade your dependencies to the actual version of core-js."

Please consider using one of the better solutions below.

Attila

npm install --save core-js@^2.5.0, worked for me, thanks – Ratite

Works for me too !! – Freshet

I decreased the version in package.json to "core-js": "^2.5.4", and run yarn, that worked for me. – Lactose

Worked !! Thank you – Unwarranted

Confirmed that npm install --save core-js@^2.5.0 worked for me as well – Ohg

For Angular 13, finally I succeeded to get 'ng test' working with ==> npm install --save core-js@^3.3 – Neibart

This might have been OK back in 2019 but seems very bad advice now since "core-js@<3.23.3 is no longer maintained and not recommended for usage due to the number of issues. Because of the V8 engine whims, feature detection in old core-js versions could cause a slowdown up to 100x even if nothing is polyfilled. Some versions have web compatibility issues. Please, upgrade your dependencies to the actual version of core-js." – Punkie

Answer 2

If you'd like to use version 3.0, you can add the a path to your tsconfig.json file.

{
    "compilerOptions": {
        ...
        "paths": {
            "core-js/es7/reflect": [
                "node_modules/core-js/proposals/reflect-metadata"
            ]
        }
    }
}

Note: You need check the node_modules/core-js/proposals/reflect-metadata relative path and correct it if needed in your project structure.

Retentive

Hi I've seen this also on gh erro reports but haven't managed to make it work, just got the same Module not found: Error: Can't resolve 'core-js/es7/reflect' error....does yours works? – Moffett

for me works this : "paths": { "core-js/es7/reflect": ["../node_modules/core-js/proposals/reflect-metadata"], "core-js/es6/*": ["../node_modules/core-js/es/*"] }, – Algarroba

Ran ncu which updated all my packages to the latest then used the above and it worked for me. – Drumm

I had to add "baseUrl": "." to make it works. Thanks mrapi amd Medeni baykal – Button

Answer 3

For Angular 8 (source):

Angular CLI 8.0+ manages the required Angular polyfills directly and projects will not require a direct dependency on core-js (assuming an application does not manually include additional core-js polyfills).

I've resolved by:

• removing core-js from my package.json dependencies
• removing import 'core-js/es7/reflect'; from my test.ts

Toothsome

For a similar issue this worked, but I needed to remove the references to core-js/es{6,7}/reflect from my polyfills.ts – Lang

Answer 4

The version 3.0 of core-js has some breaking changes:

https://github.com/zloirock/core-js/blob/master/docs/2019-03-19-core-js-3-babel-and-a-look-into-the-future.md

You should find a line similar to this in one of your files: import "core-js/es7/reflect";

Change it to this: import "core-js/proposals/reflect-metadata";

Catheycathi

This worked for me perfectly - error started after upgrading to angular 8 but your solution worked. – Aerosphere

This, among all the answers, was for me (Angular 11) the solution. Thank you, @Joffrey – Hydroplane

Answer 5

In my case , i just changed -->

import 'core-js/es6/reflect';
import 'core-js/es7/reflect';

to

import 'core-js/es/reflect';

and it worked..

Filibertofilibuster

Answer 6

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

For EX: import 'core-js/es7/reflect'; was changed to import 'core-js/es/reflect';

Dichromate

Can you explain a bit more? – Myoglobin

Hi Dieter, the problem is that your are looking for the "reflect" module in a wrong folder. 1- open the "polyfills.ts" in your src folder. 2 - find the line where there is a line like "import 'core-js/es7/reflect';". Here it is 7 for me, it can be something else in your case. 3- Remove the 7 like that: "import 'core-js/es/reflect';" and it should works. – Dichromate

Answer 7

The tsconfig.json solution from @medeni works, but don't copy the path before checking it by yourself. For me it had to be:

"paths": {
  "core-js/es7/reflect": ["../node_modules/@angular-devkit/build-angular/node_modules/core-js/proposals/reflect-metadata"]
}

the ../ is because tsconfig.json is extended by src/tsconfig.app.json or src/tsconfig.spec.json, so /src is the working directory.

note: I am using Angular CLI 8.1.0

Franctireur

Answer 8

I fixed it by adding this import: import 'core-js/proposals/reflect-metadata'; in my polyfills.ts file

/** Evergreen browsers require these. **/
// Used for reflect-metadata in JIT. If you use AOT (and only Angular decorators), you can remove.
import 'core-js/proposals/reflect-metadata';

Make sure you have the latest core-js update and everything should work.

Newspaperwoman

Basically the same as this answer. – Undervest

Answer 9

For angular latest version (currently -> 9) ,

compatible core-js version is "core-js": "~2.5.0".

step 1) Delete Node modules.

step 2) In package.json file, write "core-js": "~2.5.0" in dependecies object.

step 3) npm install

then It will work perfectly fine

Verrazano

Answer 10

I found possible answer. You have core-js version 3.0, and this version doesn't have separate folders for ES6 and ES7; that's why the application cannot find correct paths.

To resolve this error, you can downgrade the core-js version to 2.5.7. This version produces correct catalogs structure, with separate ES6 and ES7 folders.

To downgrade the version, simply run:

npm i -S [email protected]

Milt

Answer 11

I solved the problem by removing the number at the end of "es" in the path as in response to Module not found: Error: Can't resolve 'core-js/es7/reflect

Puppis

Answer 12

For Angular 7

From package.json remove:

"core-js": "3.6.5",

because it is part of the Angular package.

Cornuted