Front-end Javascript: Get a specific date/time from a defined Timezone.

README.md

#Front-end Timezone with javascript

Dependencies:

date-fns date-fns-timezone

##How to Run:

npm install
node index.js

index.js

const dateFNS = require('date-fns');
const dateFNSTimezone =  require('date-fns-timezone');

const { isWithinRange: isBetween } = dateFNS;
const { formatToTimeZone } = dateFNSTimezone;



const isDate = (date) => {
  return (date instanceof Date);
}

const parseToTwoDigitString = (digits) => ('0' + digits).substr(-2);

const parseTime = (time) => {
  if (!time || typeof time !== 'string' || time.indexOf(':') === -1) return 0;

  const [h,m,s] = time.split(':');
  const hours = h ? parseInt(h) : 0;
  const minutes = m ? (parseInt(m) * 60) : 0;
  const seconds = s ? parseInt(s) : 0;

  return {hours, minutes, seconds};
}

const parseTimeToSeconds = (time) => {
  
  const { hours, minutes, seconds } = parseTime(time);
  return (hours * 60 * 60) + (minutes * 60) + seconds;
}



function setTime(date, time, offset) {
  const selectedOffset = offset || '000';
  const year = date.getFullYear();
  const month = parseToTwoDigitString(date.getMonth() + 1);
  const day = parseToTwoDigitString(date.getDate());

  const { hours, minutes, seconds } = parseTime(time);
  const h = parseToTwoDigitString(hours);
  const m = parseToTwoDigitString(minutes);
  const s = parseToTwoDigitString(seconds);
  
  const dateString = `${year}-${month}-${day}T${h}:${m}:${s}Z`;
  const result = new Date(dateString);
  return result;
}

const parseTimeToHours = (time) => parseTimeToSeconds(time)  / 60 / 60;


const parseDateToUTC = (date) => {
  const utc = Date.UTC(
    date.getUTCFullYear(), 
    date.getUTCMonth(),
    date.getUTCDate(),
    date.getUTCHours(), 
    date.getUTCMinutes(), 
    date.getUTCSeconds()
  );
  return new Date(utc);
}

const setTimeForDateAtATimezone = (date, time, timezone) => {
    
  if (!isDate(date)) throw new Error('setTimeForDateAtATimezone date is not a valid date.');


  const timeInHours = parseTimeToHours(time);
  const timezoneOffset = formatToTimeZone(date, 'Z', { timeZone: timezone });
  const offsetInHours = parseTimeToHours(timezoneOffset);
  const newDate = setTime(date, time);


  return new Date(newDate.setHours(newDate.getHours() + (offsetInHours * -1)));
}

function setTimezone(date, timezone) {
  return new Date(formatToTimeZone(date, 'YYYY-MM-DDTHH:mm:ssZ', { timeZone: timezone }));
}


// if you're in LA, try a different TZ.
const TZ = 'America/Los_Angeles'; 


const now = new Date();
const currentLATime = setTimezone(now, TZ);
const locationAt9am = setTimeForDateAtATimezone(now, '09:00', TZ);
const locationAt5pm = setTimeForDateAtATimezone(now, '17:00', TZ);

const isOpen = isBetween(currentLATime, locationAt9am, locationAt5pm);


console.log('currentLATime:.....', currentLATime.toISOString(), ' in UTC');
console.log('LocationAt9am:.....', locationAt9am.toISOString(), ' in UTC');
console.log('locationAt5pm:.....', locationAt5pm.toISOString(), ' in UTC');
console.log('isOpen:............', isOpen ? 'YES' : 'NO');

package.json

{
  "name": "Front-end date time from a specific timezone.",
  "version": "1.0.0",
  "description": "Get a datetime for a specific timezone using front-end javascript",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Emerson Carvalho",
  "license": "ISC",
  "dependencies": {
    "date-fns": "^1.30.1",
    "date-fns-timezone": "^0.1.4",
  },
  "devDependencies": {
    "@types/date-fns": "^2.6.0"
  }
}