I really dont know how get the div tag in between value Which in this case is

F064

I have this Hmtl code..

<div class="product--price price--unit">
<span class="price--label label--purchase-unit">articlenumber:</span>
F064
</div>

I want to say if the F064 changes then alert what its changed to. I want something like this in either JS or JQuery

var divTagVal = $("div.product--price");
    $(divTagVal).on('change', function () {
      alert(divTagVal);
    });

So if F064 changes to F065 the it should alert "F065" but this doesnt work, what am i doing wrong ?