<style>
#kw {
width: 100px;
height: 100px;
border: 4px solid #000;
}
</style>

<script>
function function1() {
    var x = document.getElementById("a");
    var y = document.getElementById("kw");
    y.style.width = x.value;
    y.style.height = x.value;
}
</script>
<input type="text" id="a" onkeyup="function1()" style="width: 102px; margin-bottom: 10px">
<div id="kw"></div>

  
y.style.width = x.value;
y.style.height = x.value;

  
y.style.width = x.value + "px";
y.style.height = x.value + "px";