<div class="star" :class="starType">
    <span v-for="itemClass in itemClasses" :class="itemClass" class="star-item" track-by="$index"></span>
</div>

props: {
      size:{
        type:Number
      },
      score:{
        type:Number
      }
    }

starType() {
        return 'star-'+this.size;
      }
  .star-48 {
    width: 20px;
    height: 20px;
    margin-right: 22px;
    background-size: 20px 20px;
    
  }
  .star-36 {
    width: 15px;
    height: 15px;
    margin-right: 6px;
    background-size: 15px 15px;
  }
  .star-24 {
    width: 10px;
    height: 10px;
    margin-right: 3px;
    background-size: 10px 10px;
  }

const LENGTH = 5;
const CLS_ON = 'on';
const CLS_HALF = 'half';
const CLS_OFF = 'off';
itemClasses() {
        let result = [];
        let score = Math.floor(this.score*2)/2;
        let hasDecimal = score%1 !== 0;
        let integer = Math.floor(score);
        for (var i = 0; i < integer; i++) {
          result.push(CLS_ON);
        }
        if(hasDecimal) {
          result.push(CLS_HALF);
        }
        while (result.length<LENGTH) {
          result.push(CLS_OFF);
        }
        return result;
      }

.star-48 .on {
    background-image: url('star48_on@2x.png')
  }
  .star-48 .half {
    background-image: url('star48_half@2x.png')
  }
  .star-48 .off {
    background-image: url('star48_off@2x.png')
  }

<template>
 <div class="star" :class="starType">
  <span v-for="itemClass in itemClasses" :class="itemClass" class="star-item" track-by="$index"></span>
 </div>
</template>

<script type="text/javascript">
 const LENGTH = 5;
 const CLS_ON = 'on';
 const CLS_HALF = 'half';
 const CLS_OFF = 'off';
 export default {
  props: {
   size:{
    type:Number
   },
   score:{
    type:Number
   }
  },
  computed:{
   starType() {
    return 'star-'+this.size;
   },
   itemClasses() {
    let result = [];
    let score = Math.floor(this.score*2)/2;
    let hasDecimal = score%1 !== 0;
    let integer = Math.floor(score);
    for (var i = 0; i < integer; i++) {
     result.push(CLS_ON);
    }
    if(hasDecimal) {
     result.push(CLS_HALF);
    }
    while (result.length<LENGTH) {
     result.push(CLS_OFF);
    }
    return result;
   }

  }
 };
</script>
<style type="text/css">
 .star {
  font-size: 0;
 }
 /* .star-48 {
  width: 20px;
  height: 20px;
  margin-right: 22px;
  background-size: 20px 20px;
  
 } */
 .star-48 : last-chlid {
  margin-right: 0;
 }
 .star-48 .on {
  background-image: url('star48_on@2x.png')
 }
 .star-48 .half {
  background-image: url('star48_half@2x.png')
 }
 .star-48 .off {
  background-image: url('star48_off@2x.png')
 }
 .star-36 {
  width: 15px;
  height: 15px;
  margin-right: 6px;
  background-size: 15px 15px;
 }
 .star-36 .no {
  background-image: url('star36_on@2x.png')
 }
 .star-36 .half {
  background-image: url('star36_half@2x.png')
 }
 .star-36 .off {
  background-image: url('star36_off@2x.png')
 }
 .star-24 {
  width: 10px;
  height: 10px;
  margin-right: 3px;
  background-size: 10px 10px;
 }
 .star-24 .no {
  background-image: url('star24_on@2x.png')
 }
 .star-24 .half {
  background-image: url('star24_half@2x.png')
 }
 .star-24 .off {
  background-image: url('star24_off@2x.png')
 }
 .star-item {
  display: inline-block;
  background-repeat: no-repeat;
  width: 20px;
  height: 20px;
  margin-right: 22px;
  background-size: 20px 20px;

 }
</style>