Format javascript Date object with template string

formatDate.ts

/**
 * Formats a date as string specified by a template string
 * @param date Date to be formatted
 * @param templateString Template of the expected format. e.g. "YYYY-MM-DD hh:mm:ss" or "YY-M-D h:m:s" to trim leading zeros
 */
export function formatDate(date: Date, templateString: string): string {
    const year = date.getFullYear().toString();
    const shortYear = date.getFullYear().toString().substr(2, 2);
    const month = date.getMonth() < 9 ? "0" + String(date.getMonth() + 1) : String(date.getMonth() + 1);
    const shortMonth = String(date.getMonth() + 1);
    const day = date.getDate() < 10 ? "0" + date.getDate().toString() : date.getDate().toString();
    const shortDay = date.getDate().toString();
    const hours = date.getHours() < 10 ? "0" + date.getHours().toString() : date.getHours().toString();
    const shortHours = date.getHours().toString();
    const minutes = date.getMinutes() < 10 ? "0" + date.getMinutes().toString() : date.getMinutes().toString();
    const shortMinutes = date.getMinutes().toString();
    const seconds = date.getSeconds() < 10 ? "0" + date.getSeconds().toString() : date.getSeconds().toString();
    const shortSeconds = date.getSeconds().toString();

    return templateString
        .replace('YYYY', year)
        .replace('YY', shortYear)
        .replace('MM', month)
        .replace('M', shortMonth)
        .replace('DD', day)
        .replace('D', shortDay)
        .replace('hh', hours)
        .replace('h', shortHours)
        .replace('mm', minutes)
        .replace('m', shortMinutes)
        .replace('ss', seconds)
        .replace('s', shortSeconds)
}