html - Javascript: Disable button on Drop Down Select -

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i have dropdown menu couple of values link functions. have textbox , submit button. want if value in drop down box selected disables or hides submit button , possibly textbox made blank , once value selected turns both on.

my html code:

<body>      <p><label>drawing tool: <select id="dtool">          <option value="line">line</option>          <option value="rect">rectangle</option>          <option value="pencil">pencil</option>         <option value="eraser">eraser</option>       </select></label></p>

//some canvas code

<form id="frmcolor">         <input type='color' id='color' />     </form>         <input type='submit' value='change color' id="colorsubmit"/>

javascript in linked file called canvas.js:

...  tools.eraser = function () {     var tool = this;     this.started = false;     var varpencolor = "white";     context.strokestyle = varpencolor;     document.frmcolor.colorsubmit.disabled=true;

basically when select eraser drop down works submit button not disable.

im new js , not sure if need add sort of listener or element id ideas?

you have submit button outside of form. (as seen in example code..)

<form id="frmcolor">         <input type='color' id='color' />     </form>         <input type='submit' value='change color' id="colorsubmit"/>

should be

<form id="frmcolor">     <input type='color' id='color' />     <input type='submit' value='change color' id="colorsubmit"/> </form>

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