<!DOCTYPE html>
<html>
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<script type="text/javascript">
var subcategory = {
Mobile: ["Nokia", "Redmi", "Samsung"],
Clothes: ["Shirt", "Pant", "T-shirt"]
}
function makeSubmenu(value) {
if (value.length == 0) document.getElementById("categorySelect").innerHTML = "<option></option>";
else {
var citiesOptions = "";
for (categoryId in subcategory[value]) {
citiesOptions += "<option>" + subcategory[value][categoryId] + "</option>";
}
document.getElementById("categorySelect").innerHTML = citiesOptions;
}
}
function displaySelected() {
var country = document.getElementById("category").value;
var city = document.getElementById("categorySelect").value;
alert(country + "\n" + city);
}
function resetSelection() {
document.getElementById("category").selectedIndex = 0;
document.getElementById("categorySelect").selectedIndex = 0;
}
</script>
</head>
<body onload="resetSelection()">
<select id="category" size="1" onchange="makeSubmenu(this.value)">
<option value="" disabled selected>Choose Category</option>
<option>Mobile</option>
<option>Clothes</option>
</select>
<select id="categorySelect" size="1">
<option value="" disabled selected>Choose Subcategory</option>
<option></option>
</select>
<button onclick="displaySelected()">show selected</button>
</body>
</html>