How to compare date string using javascript

Question

I have the following string value of a date, Sun Apr 07 2019 00:00:00 GMT-0300, and I need to compare with the following date form

Answer 1

Build a date from the strings and compare the days (ie number of seconds since epoch / number of seconds in a day):

const sameDay = (dateString1, dateString2) => {
  let time1 = (new Date(dateString1)).getTime();
  let time2 = (new Date(dateString2)).getTime();
  return Math.floor(Math.abs((time1-time2))/(1000*60*60*24))==0;
}

console.log(
  sameDay('Sun Apr 07 2019 00:00:00 GMT-0300 (Horário Padrão de Brasília)','2019-04-08T03:00:00.000Z'),
  sameDay('Sun Apr 07 2019 00:00:00 GMT-0300 (Horário Padrão de Brasília)','2019-04-13T03:00:00.000Z'),
);

Answer 2

Sun Apr 07 2019 00:00:00 GMT-0300

2019-04-08T03:00:00.000Z

note that both are the same day

No, they are not.

You can convert them both to ISO string and just compare their date parts as strings (if I understood the question correctly, you want to compare date only, without time):

function isSameDate(date1, date2) {
  const [d1, ] = (new Date(date1)).toISOString().split('T');
  const [d2, ] = (new Date(date2)).toISOString().split('T');
  return d1 === d2;
}

Answer 3

Convert all the values to Date objects and compare those. Use a framework/library to do it, because parsing strings to dates manually has lots of places where it can go wrong.

Currently you are comparing the literal Strings. Because neither "2019-04-08T03:00:00.000Z", nor "2019-04-13T03:00:00.000Z" match "Sun Apr 07 2019 00:00:00 GMT-0300 (Horário Padrão de Brasília)", your second if statement fails.