I’m not sure if it’s a copy-paste issue or you’re actually making a mistake here but it seems that your innerHtml string has enters in it. It doesn’t automatically concat the values for you. You can specify a after each breakpoint. In all honesty there are alot of ways of solving this. Please see this link for some more guidance

document.getElementById("mydiv").innerHTML ="<div class='form-group'><label>Color Option</label> 
                 <select name='mycolor' onchange='javascript:fshowMe("+this+")' id='mycolor' class='form-control input-lg' required> 
                 <option value='black'>Black</option>";

document.getElementById("mydiv2").innerHTML ="<div class='form-group'><label>Color Option</label> <select name='mycolor' onchange='javascript:fshowMe("+this+")' id='mycolor' class='form-control input-lg' required><option value='black'>Black</option>";

<div id="mydiv"></div>
<div id="mydiv2"></div>

I want to add some select option tag in HTML with script below, but when select option successfully loaded, it always return without onchange='javascript:fshowMe("+this+")'

if ((xmlhttp.readyState == 4) && (xmlhttp.status == 200))
            {                 
                 document.getElementById("mydiv").innerHTML ="<div class='form-group'><label>Color Option</label>
                 <select name='mycolor' onchange='javascript:fshowMe("+this+")' id='mycolor' class='form-control input-lg' required>
                 <option value='black'>Black</option>";     
            }
            return false;

result like this

<select name="mycolor" id="mycolor" class="form-control input-lg" required="">
    <option value="black">Black</option> 

i expected the result was this

<select name="mycolor" id="mycolor" onchange="javascript:fshowMe(this)" class="form-control input-lg" required="">
    <option value="black">Black</option>

how to show the onchange to my select option?

thanks you