TypeScript: ‘super’ must be called before before accessing ‘this’ in the constructor of a derived class

Another solution I eventually came up with, in addition to the ones provided by @iberbeu and @Nypan, is to add and intermediary initProps() method right before the call to scream():

class Person 
{
    public firstName: string;

    constructor(firstName: string, props?: any)
    {
        this.firstName = firstName;
        this.initProps(props);
        this.scream();
    }

    protected initProps(props: any): void
    {
    }

    protected scream(): void
    {
        console.log(this.firstName);
    }
}

class Employee extends Person
{
    public lastName: string;

    constructor(firstName: string, lastName: string)
    {
        super(firstName, {lastName});
    }

    protected initProps(props: any): void
    {
        this.lastName = props.lastName;
    }

    protected scream(): void
    {
        console.log(this.firstName + ' ' + this.lastName);
    }
}

Although I think both made a strong point and I should actually be using a factory pattern instead..