Functional Instantiation

[sanskar-19]

🔎 Search Terms

functional instantiation, es5

🕗 Version & Regression Information

• This is a bug

⏯ Playground Link

No response

💻 Code

interface UserProfile {
    fName: string;
    lName: string;
    printFirstName: () => void;
    printLastName: () => void;
}

// Define user class
function User(this: UserProfile, fName: string, lName: string) {
    if (!(this instanceof User)) {
        return (new User(fName, lName));
    }

    this.fName = fName;
    this.lName = lName;
}

// Define prototype for print First name
User.prototype.printFirstName = function () {
    console.log(this.fName);
}

// Define prototype for print  Last name
User.prototype.printLastName = function () {
    console.log(this.lName);
}

const user = new User('John', 'Doe');

🙁 Actual behavior

new expression whose target lacks a constructor signature. Switching back to normal JS works as expected.

🙂 Expected behavior

Should compile without issues. It should point to the constructor by default present in the prototype object.

Additional information about the issue

Typescript config :

{
  "compilerOptions": {
    "target": "es2016",                             
    "module": "ESNext",                             
    "esModuleInterop": true,                        
    "forceConsistentCasingInFileNames": true,       
    "strict": true,                                 
    "outDir": "build",
    "skipLibCheck": true
  }
}

No response

[MartinJohns]

This is working as intended. See #13013 (comment).

You can add an explicit this parameter.

[sanskar-19]

This is working as intended. See #13013 (comment).

You can add an explicit this parameter.

It actually is not :
new expression whose target lacks a constructor signature.

Can you please explain this !?

As far as I know, the constructor should have been by default referred to the function prototype constructor property.

[RyanCavanaugh]

TypeScript only supports classes written with the class keyword.

[snarbies]

I imagine an interface with a construct signature could do the trick if we had Describe function signature using an interface #34319

[typescript-bot]

This issue has been marked as "Working as Intended" and has seen no recent activity. It has been automatically closed for house-keeping purposes.