JSFiddle - React, Tailwind, and code Playground

HTML

<div class="item">
    <input type = "text"  size="33"   class="uploadtxt1 url" name="txturl_1" id = "txturl_1_1" value="" />
    <input type = "text"  class="uploadtxt2" size="33" name="txtinstruction_1" id = "txtinstruction_1_1" value=""  /> <br/>
    <input type="submit" name="checkout" id="checkout"   class="graybtn1 ptr  button_float_left_checkout" disabled="disabled" value="Proceed To Checkout" />
</div>
<div class="item">
    <input type = "text"  size="33"   class="uploadtxt1 url" name="txturl_2" id = "txturl_2_2" value="" />
    <input type = "text"  class="uploadtxt2" size="33" name="txtinstruction_2" id = "txtinstruction_2_2" value=""  /> <br/>
    <input type="submit" name="checkout" id="checkout"   class="graybtn1 ptr  button_float_left_checkout" disabled="disabled" value="Proceed To Checkout" />
</div>

JavaScript

$("input[type=text]", $(".item")).change(function() {
    var allField = true;
    $(this).closest(".item").find("input[type=text]").each(function() {
         allField = allField && ($(this).val().length > 0)
    });
    if(allField) {
        $(this).closest(".item").find("input[type=submit]").prop('disabled', false);
    }
});