如何将 vif 与 Vue.js 中的值进行比较

你的html有语法问题，应该是:

<span v-for="role in user.roles">
    <span v-if="role.name == 'Admin'">Yes</span>
    <span v-else>-</span>
</span>

不过，对于用户拥有的每个角色，您仍将有额外的跨度.

使用方法判断用户是否具有管理员角色更简单，这样您就不会有额外的html:

<div id="container">
  <table>
    <tr>
      <th>User</th>
      <th>Admin</th>
      <th></th>
    </tr>
    <tr v-for="user in users">
      <td>
        {{user.first_name}} {{user.last_name}}
      </td>
      <td>
        {{isAdmin(user)}}
      </td>
    </tr>
  </table>
</div>

还有javascript:

new Vue({
  el: '#container',
  data: {
    "users": [{
      "id": 3,
      "first_name": "Joe",
      "last_name": "Blogs",
      "roles": [{
        "id": 1,
        "name": "Admin",
        "created_at": "2015-12-25 15:58:28",
        "updated_at": "2015-12-25 15:58:28",
        "pivot": {
          "user_id": 3,
          "role_id": 1,
          "created_at": "2015-12-25 16:03:09",
          "updated_at": "2015-12-25 16:03:09"
        }
      }, {
        "id": 2,
        "name": "Member",
        "created_at": "2015-12-25 15:58:28",
        "updated_at": "2015-12-25 15:58:28",
        "pivot": {
          "user_id": 3,
          "role_id": 2,
          "created_at": "2015-12-25 16:03:09",
          "updated_at": "2015-12-25 16:03:09"
        }
      }],
    }]
  },
  methods: {
    isAdmin: function(user) {
      var i;
      for (i = 0; i < user.roles.length; i++) {
        if (user.roles[i].name === "Admin") {
          return "Yes";
        }
      }

      return "-";
    }
  }
});

这里的工作示例:https://jsfiddle.net/gmsa/t56oo4tw/