html - Calculate Total Onclick Javascript -


i learning javascript , still new language. in html code have 2 lists. in first select list select product want in second select amount of product require.

i have attempted write javascript code following:

  • get product value , assign variable
  • get nr of product , assign variable
  • multiply product value number of product
  • when user clicks submit display alert box total

however code not working when user click submit button message nan instead of result of total amount variable please can have @ code , tell me doing wrong

<script type="text/javascript"> function calc() {    var total;    var fruitorveg;    var nroffruit;     course = document.getelementsbyname("fruitorveg.course.value")    nroffruit = document.getelementsbyname("nroffruit")     total = fruitorveg * nroffruit;     window.alert(total) } </script>

you taking values strings (rather numbers), , weren't using "fruitorveg". (noticed later/ new comments) using names when should use id's elements want javascript data directly , specifically, , update js accordingly. try this:

function calc() {     var fruitorveg = number(document.getelementsbyid("fruitorveg").value);     var nroffruit = number(document.getelementsbyid("nroffruit").value);      var total = fruitorveg * nroffruit;      window.alert(total) }

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