change date format to dd/mm/yyyy in javascript code example

Example 1: javascript convert date to yyyy-mm-dd

// `date` is a `Date` object
const formatYmd = date => date.toISOString().slice(0, 10);

// Example
formatYmd(new Date());      // 2020-05-06

Example 2: javascript date format dd-mm-yyyy

var date_format = new Date();
    document.write(innerHTML = date_format.getMonth()+'-'+ date_format.getDate()+'-'+date_format.getFullYear());