According to this source, it is recommended to upgrade to typescript 2.3.4 or rxjs 6 alpha.

To do this, navigate to your project's package.json file and update the typescript or rxjs version as follows:

"typescript": "2.3.4"

Then run the command npm install.

Update(06/29/2017):-

Based on feedback, it seems typescript "2.4.0" is also working properly.

It has been pointed out by others that the issue arose due to the stricter type checking of generics introduced in TypeScript 2.4. This revealed an inconsistency in a RxJS type definition, which was subsequently addressed and fixed in RxJS version 5.4.2. The most optimal solution would be to simply upgrade to 5.4.2.

If upgrading to 5.4.2 is not possible for any reason, you can resort to Alan Haddad's solution of modifying the type declaration to resolve it within your own project. You can add this code snippet to your application:

// TODO: Remove this when RxJS releases a stable version with a correct declaration of `Subject`.
import { Operator } from 'rxjs/Operator';
import { Observable } from 'rxjs/Observable';

declare module 'rxjs/Subject' {
  interface Subject<T> {
    lift<R>(operator: Operator<T, R>): Observable<R>;
  }
}

His solution comes without any other side-effects and is therefore highly effective. Other proposed solutions may have more negative impacts on your project setup, making them less ideal:

• Disabling the stricter generic checks using the compiler flag --noStrictGenericChecks. While this might make things easier for your application, it could lead to inconsistent type definitions like those encountered in this particular instance with RxJS, potentially resulting in more bugs in your app.
• Skipping type checking in libraries with the --skipLibCheck flag set to true. This is not recommended as it may result in crucial type errors going unnoticed.
• Switching to RxJS 6 Alpha - given its breaking changes, this move could possibly disrupt your application in poorly documented ways, especially since it is still in alpha. Moreover, if you have dependencies such as Angular 2+, this change might not be fully supported, ultimately causing issues either now or in the future. Resolving framework-related problems could pose an even greater challenge.

In a temporary fix, you can include the following snippet in your tsconfig.json file until the RxJS team addresses the issue with TypeScript 2.4.1:

"compilerOptions": {
    "skipLibCheck": true
}

To temporarily address the issue, you can implement a workaround with Module Augmentation

Below is the code that helped resolve the problem for me. Once RxJS releases a stable version without this issue, this workaround can be removed.

// augmentations.ts
import {Operator} from 'rxjs/Operator';
import {Observable} from 'rxjs/Observable';

// NOTE: Delete this section once a bug-free version of RxJS is available.
declare module 'rxjs/Subject' {
  interface Subject<T> {
    lift<R>(operator: Operator<T, R>): Observable<R>;
  }
}

It may seem ironic that RxJS relies heavily on this technique to define its own structure, yet it can be widely applied to solve various issues.

Despite some limitations and imperfections, the strength of this method lies in its ability to improve existing declarations, increasing type safety without requiring a complete overhaul of the file.

"dependencies": {
"@angular/animations": "^4.3.1",
"@angular/common": "^4.3.1",
"@angular/compiler": "^4.3.1",
"@angular/compiler-cli": "^4.3.1",
"@angular/core": "^4.3.1",
"@angular/forms": "^4.3.1",
"@angular/http": "^4.3.1",
"@angular/platform-browser": "^4.3.1",
"@angular/platform-browser-dynamic": "^4.3.1",
"@angular/platform-server": "^4.3.1",
"@angular/router": "^4.3.1",
"core-js": "^2.4.1",
"rxjs": "^5.4.2",
"ts-helpers": "^1.1.1",
"zone.js": "^0.7.2"
},
"devDependencies": {
"@angular/compiler-cli": "^2.3.1",
"@types/jasmine": "2.5.38",
"@types/node": "^6.0.42",
"angular-cli": "1.0.0-beta.28.3",
"codelyzer": "~2.0.0-beta.1",
"jasmine-core": "2.5.2",
"jasmine-spec-reporter": "2.5.0",
"karma": "1.2.0",
"karma-chrome-launcher": "^2.0.0",
"karma-cli": "^1.0.1",
"karma-jasmine": "^1.0.2",
"karma-remap-istanbul": "^0.2.1",
"protractor": "~4.0.13",
"ts-node": "1.2.1",
"tslint": "^4.3.0",
"typescript": "^2.3.4",
"typings": "^1.3.2"
}

in package.json "rxjs": "^5.4.2", and "typescript": "^2.3.4", then run npm install followed by ng serve to see it in action.

Adding a bit more context to share my perspective.

The issue arises when updating Typescript to the most recent version, which at the time was TypeScript 2.4.1, [ "and we always welcome upgrades :)" ], and as highlighted by @Jonnysai in their answer with relevant information shared in this link. There is an extensive discussion about the problem and its solutions.

What resolved the issue for me:
1. Initially removing TypeScript 2.4.1 first by navigating to Control Panel > Programs and Features...
2. Reinstalling TypeScript 2.4.0 from scratch and ensuring that your package.json file contains the specified

https://i.stack.imgur.com/QNMHs.jpg
configuration, elaborated further here.
You can obtain TypeScript 2.4.0 specifically designed for Visual Studio 2015 from this source.

To bypass this issue in TypeScript 2.4, you can temporarily utilize the --noStrictGenericChecks flag.

You have the option of using --noStrictGenericChecks directly on the command line, or specifying "noStrictGenericChecks": true within the "compilerOptions" section of your tsconfig.json file.

It is worth noting that RxJS 6 will address this particular problem.

If you are looking for a solution to a similar issue, check out this question: How do I get around this error in RxJS 5.x in TypeScript 2.4?

To fix the issue, insert "noStrictGenericChecks": true into the tsconfig.json configuration file under the "compilerOptions" section as displayed in the image below. After making this change, rebuild your application to apply the modifications. I encountered the same error and it was resolved after adding this setting. https://i.stack.imgur.com/I97O2.jpg

Please update the specified line in the Subject.d.ts file:

lift<R>(operator: Operator<T, R>): Observable<T>;

to:

lift<R>(operator: Operator<T, R>): Observable<R>;

The new return type should most likely be Observable<R> instead of Observable<T>

Ensure the noStrictGenericChecks setting remains true in the tsconfig.json file

{
    "compilerOptions": {
        "noStrictGenericChecks": true
    }
}

Encountering a similar issue, I was able to resolve it by utilizing the version "rxjs": "5.4.1" and "typescript": "~2.4.0", along with including "noStrictGenericChecks": true in the tsconfig.json file.

As we look forward to the release of RxJS 6, a simple workaround for this issue is to utilize the noStrictGenericChecks compiler option.

To implement this solution, navigate to your tsconfig.json file and add it under the compilerOptions, setting its value to true.

{
    "compilerOptions": {
        "noStrictGenericChecks": true
    }
}

If you prefer using the command line, include --noStrictGenericChecks.

The reason behind this complication:

In TypeScript 2.4, there was a change in strictness which caused Subject not to lift to the correct Observable. The appropriate signature should have been

(operator: Operator) => Observable

Rest assured, this issue will be resolved in the upcoming RxJS 6 version.

Access the Package.json file and make adjustments to the following settings

...
  "rxjs": "6.0.0",
  "typescript": "~2.7.2"
...

This modification should solve the issue

Although initially the above solution didn't work, I was able to resolve the issue by following this method: How can I fix the error "Subject incorrectly extends Observable" in TypeScript 2.4 and RxJs 5

This approach not only fixed the problem, but it also mentioned that the bug has been addressed in RxJs 6. So my workaround was just a temporary solution. This helped me to successfully run a fantastic example (which compiled fine previously but had an error during loading): Creating an Angular 4 application using Bootstrap 4 and TypeScript

To reinstall rxjs, run the command: npm install rxjs@6 rxjs-compat@6 --save

There is no longer a need for the ionic-native module, only @ionic-native/core is required now. Execute the following command to remove it:

npm uninstall ionic-native --save

This should resolve any issues you may be experiencing.

Simply include the following code snippet in your tsconfig.json file:

"noStrictGenericChecks": true

This will disable strict generic checks for TypeScript.

Big thank you to zmag and Rahul Sharma for providing the solution that actually works! @zmag @Rahul Sharma

  "rxjs": "5.4.1",
  "typescript": "~2.4.0"

I'm currently facing an issue:

typings/globals/core-js/index.d.ts:3:14 - error TS2300: Duplicate identifier

To resolve this problem, follow these steps:

Open your Package.json file and update the configuration as shown below:

  "rxjs": "5.4.1",
  "typescript": "~2.4.0"