这么拼接不行吗(doge)

<div class="box">
        <span><img src="/images/images1.png" alt="">span>
        <span><img src="/images/images2.png" alt="">span>
        <span><img src="/images/images3.png" alt="">span>
        <span><img src="/images/images4.png" alt="">span>
    div>
    <script>
        var bodyEl = document.body;
        var images = document.querySelector('.box').querySelectorAll('img');
        for(var i = 0;ilength;i++) {
            images[i].onclick = function(){
                bodyEl.style.backgroundImage = 'url(/images/images'+'i+1'+'.png)';
            }
        }

bodyEl.style.backgroundImage = 'url(/images/images'+(i+1)+'.png)';
i引起来就不是变量了，