javascript - Add (or multiply, subtract or divide) one var to another in JS/jQuery -

sincere apologies if has been asked , answered elsewhere, struggled finding accurate search terms this.

working in jquery have var called total. need add value of other vars total. vars in question have numerical values.

this i've tried:

var total = total+rocketspend; $(".totalamount").html(total); 

and

var newtotal = total+rocketspend; var total = newtotal; $(".totalamount").html(total); 

both have resulted in .totalamount being emptied , replaced nothing. have theories around why might going wrong - in first example var isn't allowed self defining, , in in second example browser attempts define both newtotal , total @ same time, ending in mystery. or else entirely. rocketspend var works fine on own, total before attempted addition.

thoughts?

you need use var when first define variable. looks you're trying access variable exists. example:

var total = 0; var rocketspend = 10;  total = total + rocketspend; $(".totalamount").html(total); 

additionally, try checking console errors. in browsers, can right click , inspect element or click ctrl + shift + i , clicking on console tab. can use ctrl + shift + k in firefox.