图片加载失败，使用默认图片

<div class="img-box">
    <img :src="url" />
<div>

.img-box{
    width: 100%;
    height：150px;
    position: relative
}
.img-box img:after{
    content: "";
    display: inline-block;
    position: absolute;
    z-index: 2;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: url("./default.png") no-repeat;
    background-size: 100% ;
    background-color: #fff;   
}