TS2451: Cannot redeclare block-scoped variable 'ngDevMode'.

[crowmagnumb]

I'm submitting a...

[x] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

Current behavior

From Angular 5.1.3 and before my compilation problem worked fine. Upon upgrading to 5.2.2 I now get ...

ERROR in [at-loader] ./node_modules/@angular/core/src/render3/ng_dev_mode.d.ts:9:11
TS2451: Cannot redeclare block-scoped variable 'ngDevMode'.

ERROR in [at-loader] ../module/node_modules/@angular/core/src/render3/ng_dev_mode.d.ts:9:11
TS2451: Cannot redeclare block-scoped variable 'ngDevMode'.

This is a continuation of issue 21670 with a now working repo.

Expected behavior

No compilation error.

Minimal reproduction of the problem with instructions

Check out this repo and follow the simple instructions...

https://github.com/crowmagnumb/ng-problem

What is the motivation / use case for changing the behavior?

Broken

Environment

Angular version: 5.2.1
 
For Tooling issues:
- Node version: 8.2.1
- Platform:  Mac

Others:

[rickvandermey]

I've had the same issue, because i used our own framework as a dependency. because the versions of both repo's had different angular versions i ended up with this error. When updated both repo's to the same angular version, the error disappeared.

[chuckjaz]

The problem is fundamentally here,

"paths": {
            "Utils/*": ["../module/src/utils/*"]
        }

This causes TypeScript to bring in both the @angular/core from ../modules/node_modules/@angular/core as well as the @angular/core from ./node_modules/@angular/core. This has never been supported and errors produced in this configuration are not considered regressions as the scenario is not support, it just happened not to break for you until 5.2. There are several cases where this would have broken your code earlier, you just didn't hit them.

To state this more clearly, we don't support having two different versions of angular definitions in the same compilation.

The simple way around this is to have module and app share the same copy of angular instead of having there own. In other words, move the package.json up one directory.

If you require to have a separate compilation then I recommend using something like ng-packgr to help build the module directory as a package. This package can then be installed into the node_modules of app.

We are working to improve the ergonomics of libraries and is one of our primary focuses for this release cycle. For now, however, you need to ensure that only one copy of angular is found by the compiler or separately compile the modules using ng-packgr.

[mariohmol]

Shouldnt this be open? cant solve it in this project https://github.com/mariohmol/ang-jsoneditor

This just works when angular/cli is 1.2.6 , with 1.7.x gives me this error

[mariohmol]

Got this working, if u get here follow this discussion 👍

#21670 (comment)

thanks

[tyholby]

I fixed it by updating my typescript dependency to "typescript": "2.5.3".
(I'm on "@angular/core": "5.2.8")

[jensenv]

I ran into this issue as well today, and tyholby's solution (upgrade typescript to 2.5.3) fixed it.

[jagomf]

Happening as well when upgrading from Angular 5.2 to 6.2

[mal90]

can confirm . this is happening in angular 6.0.3 as well.

[alexonaci]

Can confirm too. Happening also on angular 6.0.4

[maurei]

Same for the following:

"@angular/cli": "~6.0.8",
"@angular/compiler-cli": "^6.0.4",

[gustavogialim]

Same for the following:

"@angular/cli": "6.0.8",
"@angular/compiler-cli": "6.0.5",

[mariohmol]

have u guys tested/checked this #21670 (comment) ?

[gustavogialim]

My personal ones worked, I had a folder of node_modules in a previous project folder, this caused the error. It was this way:

Documents / project / node_modules (Correct)
Documents / node_modules (caused the error), only deleted this folder and it worked

[maurei]

Actually me it was also an error not related to angular-cli itself. I was using a custom npm library in which angular was imported. So im guessing it had to do with loading angular twice (?).

[gustavogialim]

@maurei Apparently yes, everywhere I noticed, the problem was due to two refills to the Angular, as in my case it was the duplication of the node_modules

[matheuscaldasrj]

I had an Angular Library using @angular/core 6.0.7 and when upgrade my App from Angular 5 to Angular 6 I've had this error. Looking to my package.json file I noticed that all Angular dependencies were in versions 6.0.7.

So, I changed all versions from 6.0.9 to 6.0.7 and now it works.

How is the proper way to handle with it?

[rickvandermey]

I've added some logic to delete all node modules from my specific library which gives the error in the 'postinstall' script:

var rmdir = require('rmdir');
var path = 'node_modules/{{ library }}/node_modules';

rmdir(path, (err, dirs, files) => {
	console.log(dirs);
	console.log('all files are removed');
});

[vimalans]

@rickvandermey, thanks it worked!

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