javascript function to accept multiple date formats

Question

Users want to use the following formats to enter dates:- mm-dd-yyyy OR yyyy-mm-dd OR m-d-yy OR m-d-yyyy OR mm/dd/yyyy OR m/d/yy. My plan is to capture whatever they enter and convert it to yyyy-mm-dd because that is the format that the date field value must be submitted. They have refused to use a calendar . I have tried the following JS function without any success. Any ideas?

    var value = ctrl.getValue();
    var date_input = new Date(value);
    var day = date_input.getDay();
    var month = date_input.getMonth() + 1;
    var year = date_input.getFullYear();
    var yyyy_MM_dd = year + "-" + month + "-" + day;
    return yyyy_MM_dd

Answer 1

Because its wrong to use var day = date_input.getDay();

use it like this

var day = date_input.getDate();

function getDateFormat(value){
  var date_input = new Date(value);
  var day = date_input.getDate();
  var month = date_input.getMonth() + 1;
  var year = date_input.getFullYear();
  var yyyy_MM_dd = year + "-" + month + "-" + day;
  return yyyy_MM_dd;
}
console.log(getDateFormat("2017-12-30"));
console.log(getDateFormat("12-30-2017"));

.getDay is giving you days of weeks

Also be sure to use date format accepted by Date