javascript - How to choose and work with a drop down list in js -


i got problem. created drop down list choosing algorithm work with. works first option not of them. please me?

thanks in advance

var form1 = document.getelementbyid('form1'); var form2 = document.getelementbyid('form2'); var form3 = document.getelementbyid('form3');  var formarray = [];                      formarray.push(form1.innerhtml); formarray.push(form2.innerhtml); formarray.push(form3.innerhtml);  //select drop down list//  function changetocal() {    dropdownlist.selectedindex--;    document.getelementbyid('form').innerhtml = formarray[dropdownlist.selectedindex]; }  //calculate //   document.getelementbyid('form').addeventlistener("submit",      function(event) {         var fieldy = document.getelementbyid('fieldy');         var fieldx = document.getelementbyid('fieldx');         var resultfield = document.getelementbyid('resultfield');          var x = parsefloat(fieldx.value);          var y = parsefloat(fieldy.value);           if(!fieldy.value || !fieldx.value) {         alert("please enter numbers in fields!");         } else if (dropdownlist.selectedindex = 1) {             var result = (y / 100) * x;             resultfield.innertext = "answer: " + result + "."             event.preventdefault();          } else if (dropdownlist.selectedindex = 2) {             var result = (100 / y) * x;             resultfield.innertext = "answer: " + result + "."             event.preventdefault();         } else if (dropdownlist.selectedindex = 3) {             var result = (y / x) * 100;              resultfield.innertext = "answer: " + result + " %."             event.preventdefault();                 } else {             resultfield.innertext = "error"             event.preventdefault();        }          }             );

https://codepen.io/anon/pen/vmznwq

this line:

} else if (dropdownlist.selectedindex = 1) {

needs use comparison equals operator rather assignment equals operator:

} else if (dropdownlist.selectedindex === 1) {

the other if/else clauses incorrect.

i highly recommend using decent ide, highlight potential mistakes you.

you need change this:

dropdownlist.selectedindex--; document.getelementbyid('form').innerhtml = formarray[dropdownlist.selectedindex];

to this:

document.getelementbyid('form').innerhtml = formarray[dropdownlist.selectedindex - 1];

the selectedindex live, if change using -- cause selected value updated.

the way result output assumes there <h3> id resultfield 1 of forms has id set.

other miscellaneous suggestions include...

the id attributes need unique throughout document. have 3 hidden forms , copy around html, leading 4 elements each id (resultfield, fieldx, fieldy). whether document.getelementbyid grabs right 1 down luck.

rather copying around innerhtml of forms you'd better off showing , hiding existing forms using css. alternatively use 1 form , update relevant text match current algorithm.

listening submit event of form seems odd. why not use regular button , listen click event?

if decide keep 3 forms suggest registering separate button handlers each one. fact of code inside big if/else sign need multiple functions rather single function has figure out mode in. code share factored out if appropriate.


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