Input predefined as Zero
HTML
<input type='text' class='pack' name='pack01' id='pack01' value='0'/><br>
<input type='text' class='pack' name='pack02' id='pack02' value='0'/>
JavaScript
$("input[name^=pack]").on("blur", function () {
if (!this.value) {
this.value = "0";
}
});
$("input[name^=pack]").on("focus", function () {
if (this.value = "0") {
this.value = "";
}
});