Base constructor return type 'object' is not a class or interface type.

[kikar]

TypeScript Version: 2.2.0

Got this example from the 2.2 announcement

Code

export type Constructable = new (...args: any[]) => object;

export function Timestamped<BC extends Constructable>(Base: BC) {
    return class extends Base {
        timestamp = new Date();
    };
}

Expected behavior:
Extend my class with a timestamp.

Actual behavior:
Not compiling with error: "Base constructor return type 'object' is not a class or interface type."

[agubler]

Using TS 2.2.0 (Release Candidate) the follow works as expected:

type Constructable = new (...args: any[]) => object;

function Timestamped<BC extends Constructable>(Base: BC) {
    return class extends Base {
        timestamp = new Date();
    };
}

class MyClass { }

const result = new (Timestamped(MyClass))();

// prints timestamp
console.log(result.timestamp);

[kikar]

Tried from scratch:

• created an empty project
• copied your code in index.ts
• npm i -S typescript@rc
• tsc index.ts

What I get is:

index.ts(4,26): error TS2509: Base constructor return type 'object' is not a class or interface type.

Do I need to add a tsconfig? Some special options?

[agubler]

Are you sure that tsc is the version you have just installed? what if you install the release candidate globally and try the same thing?

[kikar]

npm ls -g --depth=0

└── typescript@2.2.0

npm ls --depth=0

└── typescript@2.2.0

Also, tried with both node v6.9.4 npm v3.10.10 and node v7.5.0 npm v4.1.2

[mhegazy]

This is a duplicate of #13805. The fix for this issue was not included in typescript@2.2.0, it should be included in the next release. typescript@next should already have the fix.

[agubler]

Ha sorry I was actually using next! Apologies!

[kikar]

Why is it not going to be included in 2.2.0? Can you not make an rc1 that includes the fix?
The feature was already announced as part of 2.2.0

[mhegazy]

Why is it not going to be included in 2.2.0? Can you not make an rc1 that includes the fix?
The feature was already announced as part of 2.2.0

The next release is TS 2.2.1.