operating efficiently even when producing an incorrect output type

Exploring Typescript for the first time on Codepen.io has left me puzzled. I'm unsure why, despite defining the function signature and return type with an interface, I am able to return a different type without encountering any errors.

Is there something that I am overlooking?

Here's a snippet of the code:

interface IPerson {
    getFullName: () => void;
}

class Person implements IPerson{

constructor(
    public name: string,
    public surname: string
){}

getFullName() {
    return this.name + ' ' + this.surname;
}

}


let p = new Person('John','Doe');

console.log(p.getFullName());

Outcome:

John Doe 

Dilemma: Why does it display 'John Doe' (a string) even though I specified a void return type?

Answer №1

When using TypeScript, you may encounter a compile error message that looks something like this:

Type 'string' is not assignable to type 'void'.

Despite this error, TypeScript will still successfully compile into JavaScript. Since JavaScript does not recognize types, it will simply log the value without any regard for the return type of the function getFullName(), as the runtime has no knowledge of it.

If you prefer to prevent compilation when there are compiler errors, you can enable the noEmitOnError flag in your tsconfig.json.

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