How to allow a method to execute another method of the same Typescript class?

Question

I am working with a class that manages the registration and login of new users. Imagine that this class has two methods, the first isCharacterNameRegistered() checks if the nick already exists, and returns a boolean. The second registerNewCharacter() is responsible for making the registration, and before performing it, she also checks if the name (which can not be repeated) has already been registered. Not to repeat the same code, I thought it would be interesting to call the function isCharacterRegistered() inside registerNewCharacter() to allow or not to continue the registration. Here is the class in question:

class AuthManager {
    async isCharacterNameRegistered(characterName: string) { 
        /* verifica se o nome de personagem já é registrado, retorna true em caso afirmativo e false em caso negativo */

        const characterAlreadyRegistered = await Character.findOne({characterName})
        return !!characterAlreadyRegistered 
    }

    async registerNewCharacter(req: Request, res: Response) {
        const character = req.body

        if(this.isCharacterNameRegistered(character.characterName)) {
            return res.json({
                status: 'Erro Benigno',
                message: 'Já existe um personagem com esse nome',
                error: null
            })
        } 
    }
}

And we have a mistake, because the this inside registerNewCharacter() refers to the scope of the function in which it is evoked, not that of the class AuthManager, right? apart from the this Typescript does not compile, saying it cannot find isCharacterNameRegistered and suggests that we use the this, but as we’ve seen it doesn’t work!

What am I doing wrong? Is it possible to call one function directly within another or do I need an extra step? I thought the approach without using the this would work, because function calls within others are perfectly possible in several languages, as for example:

function dale() {
    return true
}

function dolly() {
    if(dale()) {
        console.log('dolly')
    }
}

dolly()

that works perfectly, but apparently the context of a class brings some new dynamics, because:

class Dollynho {
    dale() {
        return true
    }

    dolly() {
        if(dale()) {
            console.log('dolly')
        }
    }
}

const teste = new Dollynho

teste.dolly()

no longer works