text: class CheckingAccount {
      constructor(clientId, email, firstName, lastName) {
          this.clientId = this.setClientId(clientId);
          this.email = this.setEmail(email);
          this.firstName = this.setName(firstName, 'First');
          this.lastName = this.setName(lastName, 'Last');
      }
      isLetter(str) {
          return str.length === 1 && str.match(/[a-z]/i);
      }
      setClientId(id) {
          if (id.length !== 6 || typeof (id) !== 'string') {
              throw new TypeError('Client ID must be a 6-digit number');
          }
          return id;
      }
      setEmail(email) {
          let regex = `\w*@[A-Za-z.]{1,}`;
          if (!email.match(regex)) {
              throw new TypeError("Invalid e-mail");
          }
          return email;
      }
      setName(name, type) {
          let hasOnlyLetters = Array.from(name).every(x => this.isLetter(x));
  
          if (name.length < 3 || name.length > 20) {
              throw new TypeError(`${type} name must be between 3 and 20 characters long`)
          }
          if (!hasOnlyLetters) {
              throw new TypeError(`${type} name must contain only Latin characters`)
          }
          return name;
      }
  
  }