解决vue2.0动态绑定图片src属性值初始化时报错的问题

<template>  <div>    <img :src="imgUrl">  </div></template><script>export default {  data(){    return {      captcha_id: ""     }  },  computed: {    imgUrl(){      return ' http://www.demo.com/static/ '+ this.captcha_id + '.png'    },  },  methods: {    init(){        // 此处省略一个请求 ，假设成功返回数据为 res        this.captcha_id = res.data.captcha_id;    },  }    created(){    this.init();  }}</script><style lang="scss" scoped></style>

computed: {    imgUrl(){      if(this.captcha_id){        return this.$store.state.cmnUrl +'/v1/cmn/captcha/new/' + this.captcha_id + '.png'      }else{        return null;      }    },  },