Edit in JSFiddle

// listener
$(":input").on("keyup change", WriteFormDataToDiv);

// call on load
WriteFormDataToDiv()

function WriteFormDataToDiv() {
  var data = $(":input").serializeArray()
  var html = JSON.stringify(data, null, 2)
  $("#formdata").html(html)
}

<input type="text" name="cat"     value="frida" />
<input type="text" name="dog"     value="buddy" /><br/>
<input type="text" name="food"    value="pizza" />
<input type="text" name="dessert" value="ice cream" />

<pre id="formdata"></pre>











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pre {
  padding: 15px;
  background: lightgrey;
}