Freeze body scroll without body width jump

HTML

<div class="main longcontent">
    <button>Open Modal</button>
    <br>
    <button>Open Modal</button>
    <br>
    <button>Open Modal</button>
</div>
<div class="modal">
    <div class="longcontent">
        <button>Close Modal</button>
        <br>
        <button>Close Modal</button>
        <br>
        <button>Close Modal</button>
    </div>
</div>

CSS

.longcontent {
    margin: 25% 5%;
    line-height: 300px;
    text-align:center;
    background: green;
}
.modal {
    position: fixed;
    overflow: auto;
    top: 9%;
    right;
    9%;
    left: 9%;
    bottom: 9%;
    top: 0;
    right;
    0;
    left: 0;
    bottom: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.7);
}
.modal .longcontent {
    background: yellow;
    margin: 10% 20%;
}

JavaScript

$(function () {
    var $body = $(window.document.body);

    function bodyFreezeScroll() {
        var bodyWidth = $body.innerWidth();
        $body.css('overflow', 'hidden');
        $body.css('marginRight', ($body.css('marginRight') ? '+=' : '') + ($body.innerWidth() - bodyWidth))
    }

    function bodyUnfreezeScroll() {
        var bodyWidth = $body.innerWidth();
        $body.css('marginRight', '-=' + (bodyWidth - $body.innerWidth()))
        $body.css('overflow', 'auto');
    }

    $('.modal').hide()

    $('.longcontent.main button').click(function () {
        $('.modal').show()
        bodyFreezeScroll()
    })
    $('.modal button').click(function () {
        $('.modal').hide()
        bodyUnfreezeScroll()
    })
})