reportComplaints.js: Uncaught TypeError: Cannot read property 'message' of undefined

var tab={
    message:{
        number:‘‘,
        title:‘‘
    }
}

var id= {
    template: ‘#id‘,
    data: function(){
        return tab;
    },
    created: function () {
        //感觉问题就是这
        var self = this;
       
    },
    methods: {
            showComplaintsDetail:function(item){
                var self = this;
                self.tab.message= item; //这样写就会报那个错误
             } 
   } 
}