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status0
		resolve()
	}
}).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
	}
	
})