Date Formatter Fn

formatDate.ts

/**
 * ### Date Formatter
 * @description Given a format string, the formatter does simple replacment for date string tokens.
 * @param epoch - ISO Epoch Date number
 * @param fmt - format String
 * 
 * @token `YYYY`:Year; ex: 2021
 * @token `YY`:AbbrevYear; 21
 * @token `MM`:Month; 04
 * @token `DD`:Date; 01
 * @token `HH`:24 Hours; 13
 * @token `%H`:Am/pm Hours; 01
 * @token `hh`:Am/pm Hours; 01pm
 * @token `mm`:minutes; 59
 * @token `ss`:seconds; 42
 * @example
 * ```js
 * fmtDate('YYYYMMDDhhmmmsss')(Date.now()) // '2021040801pm27m59s'
 * ```
 */
export const fmtDate = (fmt:string = 'YYYYMMDDHH')=>{
    const p2 = (s:string)=>s.padStart(2, '0')
    return (epoch:number) => {
        const d = new Date(epoch)
        const YYYY = d.getFullYear().toString()
        const YY = p2(d.getFullYear().toString().slice(-2))
        const MM = p2((d.getMonth()+1).toString())
        const DD = p2(d.getDate().toString())
        const HH = p2(d.getHours().toString())
        const mm = p2(d.getMinutes().toString())
        const ss = p2(d.getSeconds().toString())
        const H  = p2((d.getHours() % 12).toString())
        const ampm = d.getHours() > 11 ? 'pm' : 'am'
        const hh = `${H}${ampm}`
        
        return fmt
            .replace('YYYY',YYYY)
            .replace('ampm',ampm)
            .replace('YY',YY)
            .replace('MM',MM)
            .replace('DD',DD)
            .replace('HH',HH)
            .replace('%H',H)
            .replace('mm',mm)
            .replace('ss',ss)
            .replace('hh',hh)
    }
}