Javascript Date check if a defined variable is a date

let a = new Date(); 
let b = 3.14; /*w  w  w.  j  a  va2  s.c  o m*/
let c = "I'm a string"; 

if (a instanceof Date) { 
   console.log("a is a Date"); 
} else { 
   console.log("a is not a Date"); 
} 

if (b instanceof Date) { 
   console.log("b is a Date"); 
} else { 
   console.log("b is not a Date"); 
} 

if (c instanceof Date) { 
   console.log("c is a Date"); 
} 
else { 
   console.log("c is not a Date"); 
}