html - How do I write JavaScript that validates input across multiple forms? -

i attempting write javascript traverses multiple html forms, checks input given value on edit, enables/disables submit button form based on input value.

i have simple example script, overrides onclick function of checkboxes, test flow of code.

<form>     <input type="checkbox" />     <input type="submit" disabled="disabled" /> </form> <form>     <input type="checkbox" />     <input type="submit" disabled="disabled" /> </form> <form>     <input type="checkbox" />     <input type="submit" disabled="disabled" /> </form> <form>     <input type="checkbox" />     <input type="submit" disabled="disabled" /> </form> <form>     <input type="checkbox" />     <input type="submit" disabled="disabled" /> </form> <script type="text/javascript">     forms = document.getelementsbytagname("form");     for(i=0; i<forms.length; i++)     {         inputs = forms.item(i).getelementsbytagname("input");         inputs.item(0).onclick = function()         {             if(this.checked)                 inputs.item(1).removeattribute("disabled");             else                 inputs.item(1).setattribute("disabled","disabled");         }     } </script> 

what expect happen: checkboxes change value of submit button in same form.

what happens: checkboxes change value of submit button in last form.

the actual code smarter, want understand flow of javascript code before progressing onto more complex.

thanks in advance!

try this:

document.body.onchange = function(e) {     // delegates way body - if have more specific     // container, prefer using instead.     e = e || window.event;     var t = e.srcelement || e.target;     if( t.nodename == "input" && t.type == "checkbox") {         // may want add classname checkboxes more specificity         t.parentnode.getelementsbytagname('input')[1].disabled = !t.checked;     } }; 

the reason seeing behaviour you're getting because inputs' value not fixed, repeatedly re-assigning next form's elements, resulting in last one.