++a returns the value of an after it has been incremented. It is a pre-increment operator since ++ comes before the operand.
a++ returns the value of a before incrementing. It is a post-increment operator since ++ comes after the operand.
You can try to run the following code to learn the difference between i++ and ++i −
<html> <body> <script> var a =10; var b =20; //pre-increment operator a = ++a; document.write("++a = "+a); //post-increment operator b = b++; document.write("<br> b++ = "+b); </script> </body> </html>