//html
    <div class="mobile-pay-number">
        <div id="buyNumber" class="mui-slider-handle">
            <span></span>
            <div class="mui-numbox mui-right" data-numbox-min="1">
                <button class="mui-btn mui-btn-numbox-minus" type="button">-</button>
                <input class="mui-input-numbox" type="number" />
                <button class="mui-btn mui-btn-numbox-plus" type="button">+</button>
            </div>
        </div>
    </div>
        //JS
        //
        mui(".mui-input-numbox")[0].addEventListener("change", function () {
            console.log(mui("-sharpbuyNumber").numbox().getValue());
            mui(".m-p-j-paynumber")[0].innerHTML = (mui(".pay-spjg")[0].outerText * mui(".mui-input-numbox")[0].value) - mui(".m-p-j-dy")[0].outerText;
        });

when you click to increase the quantity for the first time, the growth value is fine, as shown in figure

2

then click +-both are two steps

what"s the problem with boss