html - Cannot read property '0' of undefined -- JavaScript -

my goal: upon checking checkbox, pertinent element enabled.

this javascript. understand it, this input. calling parentnode on going checkbox div. set parent_1 col-md-3 div. set child next sibling parent_1, next col-md-3 div. error

uncaught typeerror: cannot read property '0' of undefined  

the error location input.

function selectelement(object) {     var parent = object.parentnode;     var parent_1 = parent.parentnode;     var child = parent_1.nextsibling;     if (parent.children[0].checked == true) {         child.children[0].disabled = false;     }      else {         child.children[0].disabled = true;     } } 

this html:

<div class="col-md-3">     <div class="checkbox checkbox-primary">         <input type="checkbox" id="fast_dd" onclick="selectelement(this);">         <label for="fast_dd">anomalies</label>     </div> </div> <div class="col-md-3">     <select name="fast" class="selectpicker" disabled>         <option>options</option>     </select> </div> 

edit - not @ sure why wrote parent.children[0] instead of object, clumsy of me

edit 2 - changed title more accurate

you there.

what want next element, not next dom node (which text node).

use js instead:

function selectelement(object) {     var parent = object.parentnode;     var parent_1 = parent.parentnode;     var child = parent_1.nextelementsibling; //nextelementsibling instead of nextelement     if (object.checked == true) { // use object instead of parent.children         child.children[0].disabled = false;     }      else {         child.children[0].disabled = true;     } } 

here fiddle: http://jsfiddle.net/1hzmwd7w/2/