JSFiddle - React, Tailwind, and code Playground

JavaScript

alert(ConvertJsonDateString("\/Date(1280635200000-0400)\/"));

function ConvertJsonDateString(jsonDate) {  
   var shortDate = null;    
   if (jsonDate) {  
       var regex = /-?\d+/;  
       var matches = regex.exec(jsonDate);  
       var dt = new Date(parseInt(matches[0]));  
       var month = dt.getMonth() + 1;  
       var monthString = month > 9 ? month : '0' + month;  
       var day = dt.getDate();  
       var dayString = day > 9 ? day : '0' + day;  
       var year = dt.getFullYear();  
       shortDate = monthString + '/' + dayString + '/' + year;  
}  
return shortDate;  
};