$remove is not a function

var vm = new Vue({    
    el: "#app",
    data: {        
        title: "",
        price: "",
        areas: "",
        extendItem: [{name: "Test", value: "test"}],
        industry: "",
        detailed: "",
        isCommission: false,
        commission: "",
        desc: ""    
      },
    methods: {        
      addExtend: function () {            
        this.extendItem.push({name: "", value: ""});        
      },
      delExtend: function (item) {            
        this.extendItem.$remove(item);        
      }    
    }
});