Extend the TypeScript Date Object with some useful methods

date.extensions.ts

/**
 * Fork of: https://gist.github.com/weslleih/b6e7628416a052963349494747aed659
 * Important notice: when using with node you need the package `full icu` installed and configured or compile node with full-icu support.
 * This way the compiled js code can run using language data other then `en-us`.
 */
export {}

declare global {
    interface Date {
        addDays(days: number, useThis?: boolean): Date;
        isToday(): boolean;
        clone(): Date;
        isAnotherMonth(date: Date): boolean;
        isWeekend(): boolean;
        isSameDate(date: Date): boolean;
        getStringDate(): String;
}
}

//TODO: collect language data.
let translatedTerms = new Map([
    ['en-us', {'today': 'Today', 'tomorrow': 'Tommorow', 'yesterday': 'Yesterday', 'conective': 'of'}],
    ['pt-br', {'today': 'Hoje', 'tomorrow': 'Amanhã', 'yesterday': 'Ontem', 'conective': 'de'}]
]);

Date.prototype.addDays = function (days: number): Date {
    if (!days) return this;
    let date = this;
    date.setDate(date.getDate() + days);

    return date;
};

Date.prototype.isToday = function (): boolean{
    let today = new Date();
    return this.isSameDate(today);
};

Date.prototype.clone = function (): Date{
    return new Date(+this);
};

Date.prototype.isAnotherMonth = function (date: Date): boolean {
    return date && this.getMonth() !== date.getMonth();
};

Date.prototype.isWeekend = function (): boolean  {
    return this.getDay() === 0 || this.getDay() === 6;
};

Date.prototype.isSameDate = function (date: Date): boolean  {
    return date && this.getFullYear() === date.getFullYear() && this.getMonth() === date.getMonth() && this.getDate() === date.getDate();
};

Date.prototype.getStringDate = function (locale = 'en-us', overrides = {}): String {
    let terms = Object.assign(translatedTerms.get(locale) || {}, translatedTerms.get('en-us'), overrides);
    let today = new Date();
    let monthName = new Intl.DateTimeFormat(locale, {'month': 'long'}).format(this);
    if (this.getMonth() == today.getMonth() && this.getDay() == today.getDay()) {
        return terms.today;
    } else if (this.getMonth() == today.getMonth() && this.getDay() == today.getDay() + 1) {
        return terms.tomorrow;
    } else if (this.getMonth() == today.getMonth() && this.getDay() == today.getDay() - 1) {
        return terms.yesterday;
    } else {
        return `${this.getDay()} ${terms.conective} ${monthName} ${terms.conective} ${this.getFullYear()}`;
    }
}