JSFiddle - React, Tailwind, and code Playground

HTML

<select size="1" id="part_1">
<option value="var1">var1</option>
<option value="var2">var2</option>
<option value="var3">var3</option>
</select>
<select size="1" id="part_2">
<option value="var4">var1</option>
<option value="var5">var2</option>
<option value="var6">var3</option>
</select>
<img id="target">

CSS

img {
  width:100%;
  height:100%;
}

body {
  min-height:100%;
}

JavaScript

$("select").on('change',()=>{
	var part_1=$('#part_1').val();
  var part_2=$('#part_2').val();
  var link = 'http://my-site/'+part_1+'_'+part_2+'.jpg';
  $("#target").attr('src',link);
  $("#target").attr('alt',link);
  
});