Learn TypeScript 3 by Building Web Applications

Implementing the displayCountries method

The displayCountries method receives an array of Country objects and renders those as <option> HTML elements as follows:

displayCountries(countries: Country[]): void { 
    if (!countries) { 
        throw new Error("The list of countries to display must be         provided!"); 
    } else if (countries.length === 0) { 
        throw new Error("The list of countries cannot be empty!"); 
    } 

    console.log("Displaying the countries"); 
    let countriesOptions = ""; 
    countries.forEach(country => { 
        countriesOptions += `<option         value="${country.id}">${country.name}</option>`; 
    }); 
    this._countrySelect.innerHTML = countriesOptions; 
} 

Nothing special to mention here; this is a technique that we've already used before.

If you want to improve the code, ...