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思路

利用css动画和js定时器（setTimeout），实现简单的进度条。

优势

不使用 setInterval，减少js代码量，业务代码更加简洁。

示意图

上传中	上传成功	上传失败

代码

html

<!-- img-wrap有两种状态：uploading（上传中）、uploadfailed（上传失败）-->
<div class='img-wrap uploading'><img src='' alt='' /><div class='img-state'><!-- progress-bar 有三种状态：progress-bar-status0、progress-bar-status1、progress-bar-status2--><div class='progress-bar'><div class='progress-innerbar'></div></div></div>
</div>

scss

.img-wrap {/*上传中、上传失败*/&.uploading, &.uploadfailed {/*黑色遮罩*/&::before {content: "";position: absolute;left: 0;right: 0;top: 0;bottom: 0;margin: auto;background: rgba(0,0,0,0.3);}			 }.img-state {/*底部进度条*/.progress-bar {width: 8.8rem;height: 0.4rem;position: absolute;left: 0;right: 0;bottom: 0.6rem;margin: auto;border-radius: 0.2rem;background: rgba(255,255,255,0.72);/*底部进度条（内部）*/.progress-innerbar {width: 0;height: 0.4rem;background: #FF5500;border-radius: 0.2rem;}/*进度条初始状态*/&.progress-bar-status0 {.progress-innerbar {width: 20%;-webkit-transition: width .5s linear;-moz-transition: width .5s linear;-o-transition: width .5s linear;transition: width .5s linear;  /*动画时长500ms*/}}/*上传失败，进度条60%*/&.progress-bar-status1 {.progress-innerbar {width: 60%;-webkit-transition: width .5s linear;-moz-transition: width .5s linear;-o-transition: width .5s linear;transition: width .5s linear;  /*动画时长500ms*/}}/*上传成功，进度条100%*/&.progress-bar-status2 {.progress-innerbar {width: 100%;-webkit-transition: width .5s linear;-moz-transition: width .5s linear;-o-transition: width .5s linear;transition: width .5s linear;  /*动画时长500ms*/}}}}/*上传失败*/&.uploadfailed .img-state::after {content: "上传失败";position: absolute;left: 0;right: 0;top: 50%;margin: auto;-webkit-transform: translateY(-50%);transform: translateY(-50%);display: block;font-size: 1.1rem;line-height: 2rem;text-align: center;color: #fff;}
}

js

new Promise((resolve) => {// 执行上传图片方法uploadImage(base64) {$('.progress-bar').addClass("progress-bar-status0"); // 开始上传，进度条状态变成status0resolve()}
}).then((result) => {// 上传成功if(result.rc == 1) {// 上传成功，进度条状态变成status2$('.progress-bar').removeClass("progress-bar-status0 progress-bar-status1").addClass("progress-bar-status2");setTimeout(() => {$('.img-wrap').removeClass("uploading uploadfailed");$('.img-wrap').find('.img-state').remove();}, 500)  // 假延时500ms，因为css动画需要500ms} // 上传失败else {// 上传失败，进度条状态变成status1$('.progress-bar').removeClass("progress-bar-status0 progress-bar-status2").addClass("progress-bar-status1");setTimeout(() => {$('.img-wrap').removeClass("uploading").addClass("uploadfailed");}, 500)  // 假延时500ms，因为css动画需要500ms}})