form.html

<form id="new_size">
<input type="text" name="size_name" id="size_input" />
<input type="submit" />
</form>

<script>

$(document).ready(function() {
     
     $("#new_size").submit(function(evt) {

            evt.preventDefault();

            console.log( "size-input": $("#size_input").val() );
     });
});
</script>