[Solved] How do I format a date in JavaScript?

Question

For custom-delimited date formats, you have to pull out the date (or time)
components from a DateTimeFormat object (which is part of the
ECMAScript Internationalization API), and then manually create a string
with the delimiters you want.

To do this, you can use DateTimeFormat#formatToParts. You could
destructure the array, but that is not ideal, as the array output depends on the
locale:

{ // example 1
   let f = new Intl.DateTimeFormat('en');
   let a = f.formatToParts();
   console.log(a);
}
{ // example 2
   let f = new Intl.DateTimeFormat('hi');
   let a = f.formatToParts();
   console.log(a);
}

Better would be to map a format array to resultant strings:

function join(t, a, s) {
   function format(m) {
      let f = new Intl.DateTimeFormat('en', m);
      return f.format(t);
   }
   return a.map(format).join(s);
}

let a = [{day: 'numeric'}, {month: 'short'}, {year: 'numeric'}];
let s = join(new Date, a, '-');
console.log(s);

You can also pull out the parts of a DateTimeFormat one-by-one using
DateTimeFormat#format, but note that when using this method, as of March
2020, there is a bug in the ECMAScript implementation when it comes to
leading zeros on minutes and seconds (this bug is circumvented by the approach
above).

let d = new Date(2010, 7, 5);
let ye = new Intl.DateTimeFormat('en', { year: 'numeric' }).format(d);
let mo = new Intl.DateTimeFormat('en', { month: 'short' }).format(d);
let da = new Intl.DateTimeFormat('en', { day: '2-digit' }).format(d);
console.log(`${da}-${mo}-${ye}`);

When working with dates and times, it is usually worth using a library (eg. luxon, date-fns, ~~moment.js~~ is not recommended for new projects) because of the many hidden complexities of the field.

Note that the ECMAScript Internationalization API, used in the solutions above
is not supported in IE10 (0.03% global browser market share in Feb
2020).

Accepted Answer