var regularExpressionForURL = /^https?:\/\//i;
var originalURL1 = "https://www.example.com/index";
var originalURL2 = "/index";
if (regularExpressionForURL.test(originalURL1)) {
   console.log("This is absolute URL");
}
else {
   console.log("This is relative URL");
}
if (regularExpressionForURL.test(originalURL2)) {
   console.log("This is absolute URL");
}
else {
   console.log("This is relative URL");
} 

node fileName.js.

PS C:\Users\Amit\javascript-code> node demo266.js
This is absolute URL
This is relative URL