vue实现文字展开收起

思路：
主要是css上可以分为两部分，第一部分展示前面两行，第二部分会根据第一部分的行数判断缩进的大小，然后展示第三行。最后通过背景色的控制让两者看上去是一段文字。
html

<div :class="showTotal ? 'total-introduce' : 'detailed-introduce'">
  <div class="intro-content" :title="introduce" ref="desc">
       <span class="merchant-desc"  v-if="introduce">{{introduce}}</span>
       <div class="unfold" @click="showTotalIntro" v-if="showExchangeButton">
           <p>{{exchangeButton ? '展开' : '收起'}}</p>
       </div>
   </div>
</div>

css

.total-introduce{
  height: auto;
   overflow: hidden;
   font-size: 26px;
   color: #666;
   margin-top: 30px;
   .intro-content{
       .merchant-desc{
           width: 100%;
           line-height: 40px;
       }
   }
   .unfold{
       display: block;
       float: right;
       width: 80px;
       height: 40px;
       z-index: 8;
       text-align: center;
       p{
           margin: 0;
           line-height: 40px;
           color: #0098ff;
       }
   }
}
.detailed-introduce{
    font-size: 26px;
    color: #666;
    position: relative;
    overflow: hidden;
    margin-top: 30px;
    .intro-content{
    	//最大高度设为3倍的行间距
        max-height: 120px;
        line-height: 40px;
        word-wrap: break-word;
        word-break: break-all;
        background-color: #fff;
        color: #fff;
        overflow: hidden;
        .merchant-desc{
            width: 100%;
            line-height: 40px;
        }
        &::after,
        &::before{
            content: attr(title);
            position: absolute;
            left: 0;
            top: 0;
            width: 100%;
            color: #666;
        }
        &::before{
            display: block;
            overflow: hidden;
            z-index: 1;
            max-height: 80px;
            background: #FFF;
        }
        &::after{
            display: -webkit-box;
            -webkit-box-orient: vertical;
            height: 120px;
            // 截取行数
            -webkit-line-clamp: 3;
            text-overflow: ellipsis;
            box-sizing: border-box;
            // 行首缩进字符数，值为[(截取行数-1)*尾部留空字符数]
            text-indent: -6em;
            // 尾部留空字符数
            padding-right: 3em;

        }
        .unfold {
            z-index: 8;
            width: 80px;
            height: 40px;
            outline: 0;
            position: absolute;
            right: 0;
            bottom: 0;
            text-align: center;
            p {
                margin: 0;
                color: #0098ff;
            }
        }
    }
}

js

export default {
 data() {
    return {
     introduce = ''; // 简介
     showTotal = true; // 简介全部显示
     exchangeButton = true; // 展开/收起文字改变
     showExchangeButton = false; // 是否显示 展开/收起 文字
    }
 },
 methods: {
 	showTotalIntro() {
      this.showTotal = !this.showTotal;
      this.exchangeButton = !this.exchangeButton;
    }
 },
 watch: {
	 introduce: function(){
	 	this.$nextTick(() => {
           if (!this.$refs.desc) {
                return;
            }
            const descHeight = window.getComputedStyle(this.$refs.desc).height.replace('px', '');
            if (parseInt(descHeight) * 2 > 120) {
                this.showExchangeButton = true;
                this.exchangeButton = true;
                this.showTotal = false;
            } else {
                this.showExchangeButton = false;
                this.showTotal = true;
            }
        });
	 }
}