add and assignment(+=) operator
The add and assignment(+=) operator reduces the code little bit.It may not much influential in small codes whereas coming to long codes it's use can't be ignored.
Example
<html> <body> <script> var tot = 0; var a = [1,45,78,9,78,40]; for(var i = 0; i<a.length;i++){ tot += a[i] } document.write(tot); </script> </body> </html>
Output
251