Function that return me the previous day

Question

Can you help me with this problem? I tried to make a function that receives a parameter of type Date e.g. 12.11.2020. I want it to return the previous day.

function getPreviousDay(d) {
  var dateObj = new Date(d);
  var previousDay = dateObj.setDate(dateObj.getDate() - 1);
  return previousDay;
}

console.log(getPreviousDay(new Date())); //1606809601830

But as you see, the function returns: 1606809601830, I don't know why. Thank you, guys!

Answer 1

You don't want to return the result of Date.prototype.setDate() which is the date in milliseconds, you want to return the mutated dateObj

function getPreviousDay(d) {
  var dateObj = new Date(d);
  dateObj.setDate(dateObj.getDate() - 1);
  return dateObj ;
}

console.log(getPreviousDay(new Date()));

Answer 2

A simple ES6 one-liner would be :

const getPreviousDay = d => d.setDate(d.getDate() - 1) && d

console.log(getPreviousDay(new Date())); 

This function changes the day of the Date object you pass it, and returns it. No need to create an intermediary one.

Typescript version (with type checking, to make sure you always pass it a Date object, and not a string) :

const getPreviousDay = (d:Date): Date => d.setDate(d.getDate() - 1) && d

Answer 3

This code return like this yesterday date(1.12.2020).

function getPreviousDay(d) {
  var dateObj = new Date(d);
  dateObj.setDate(dateObj.getDate()-1);
  return dateObj.getDate() + '.' + (dateObj.getMonth()+1) + '.' + dateObj.getFullYear();
}

console.log(getPreviousDay(new Date()));