關(guān)于兩個(gè)setInterval 替換<img>.url和<div>.background的問題

<div id="loading_bg" style="background:url("img/loading/loading_bg0.png") no-repeat;background-size: cover;">
    <img src="img/loading/loading_icon0.png" alt="" id="loading_icon">
</div>

<----------------->

var bgCount = 0;var iconCount = 0;
setInterval(changbg,100);
function changbg() {
    document.getElementById('loading_bg').setAttribute('style','background:url("img/loading/loading_bg'+bgCount%7+'.png") no-repeat;background-size:cover;');
    bgCount++;
}
setInterval(changeicon,100);
function changeicon() {
    document.getElementById('loading_icon').setAttribute('src','img/loading/loading_icon'+iconCount%3+'.png');
    iconCount++;
}

問題是

img.src的圖片一致持續(xù)在循環(huán)請(qǐng)求，然而外層的div.background.url并沒再請(qǐng)求。
請(qǐng)問這是什么原因？以及如何解決循環(huán)加載的問題？
扣謝~