<input id="postalcode" type="text"/>
<div>
↑に郵便番号を入力
</div>
<p>
unmask:<span id="unmask"></span>
</p>
#postalcode { width: 10rem }
body { margin: 10px }
var element = document.getElementById('postalcode');
var maskOptions = {
mask: '000-0000'
};
var mask = IMask(element, maskOptions);
element.addEventListener("input", e => {
document.getElementById("unmask").innerText = mask.unmaskedValue;
});