Learn TypeScript 3 by Building Web Applications

Implementing the displayYears method

This method is very similar:

displayYears(years: number[]): void { 
    if (!years) { 
        throw new Error("The list of years must be provided!"); 
    } else if (years.length === 0) { 
        throw new Error("The list of years cannot be empty!"); 
    } 

    console.log("Displaying the years"); 
    let fromYearOptions = ""; 
    years.forEach(year => { 
        fromYearOptions += `<option value="${year}">${year}</option>`; 
    }); 

    // reverse order 
    let toYearOptions = ""; 
    years.reverse().forEach(year => { 
        toYearOptions += `<option value="${year}">${year}</option>`; 
    });     this._fromYearSelect.innerHTML = fromYearOptions; 
    this._toYearSelect.innerHTML = toYearOptions; 
} 

The only thing to notice here is that, in order to build toYearOptions, we iterate through ...