https://jsfiddle.net/c2wjmuxp/3/
<div class="field-wrapper" id="target">
<input type="text" class="full-width"/>
</div>
<div>
<input type="range" min="0" step="1" max="100" value="100" id="control">
</div>
<style>
*{
box-sizing:border-box;
}
.field-wrapper{
padding:10px;
background:#EEE;
}
.full-width{
display:block;
width:100%;
padding:10px 20px;
}</style>
<script>
var target=document.querySelector('#target');
document.querySelector('#control').addEventListener('input',function(){
target.style.width=this.value+'%';
});
</script>