JavaScript和TypeScript范围问题

Question

我正在尝试使用typescript，Knockout和azure移动服务来获取一些数据。问题是当我从azure获取数据时，它是异步的，我无法再获取viewmodel对象。我认为这是一些范围/关闭问题，请帮我找到解决方案。它在Done（）的回调函数中为null;

这里是我的打字稿代码：

class pmViewModel { 
    public welcomeMsg: string; 
    public totalCount: number; 
    constructor() { 
     this.welcomeMsg = ""; 
    } 
} 

class Manager { 
    client: any; 
    portalVM: pmViewModel; 
    constructor() { 
     this.client = new WindowsAzure.MobileServiceClient("url", "key"); 
     this.portalVM = new pmViewModel(); 
    } 

    LoadData() { 
     console.log("load data for management portal"); 
     this.portalVM.welcomeMsg = "Hello"; 
     this.portalVM.totalCount = 0; 
     var dataTable = this.client.getTable('dataTable'); 

     dataTable.take(1).includeTotalCount().read().done(this.populateTotal,this.portalVM); 

     ko.applyBindings(this.portalVM); 
     }; 

     populateTotal(result, vm) { 
      console.log(result); 
      console.log(vm); //null here 
      this.portalVM.totalCount = 100000;////this is also null 
     } 
} 

和生成的JavaScript代码：

var pmViewModel = (function() { 
    function pmViewModel() { 
     this.welcomeMsg = ""; 
    } 
    return pmViewModel; 
})(); 
var Manager = (function() { 
    function Manager() { 
     this.client = new WindowsAzure.MobileServiceClient("url", "key"); 
     this.portalVM = new pmViewModel(); 
    } 
    Manager.prototype.LoadData = function() { 
     console.log("load data for management portal"); 
     this.portalVM.welcomeMsg = "Hello"; 
     this.portalVM.totalCount = 0; 
     var dataTable = this.client.getTable('dataTable'); 
     dataTable.take(1).includeTotalCount().read().done(this.populateTotal, this.portalVM); 
     ko.applyBindings(this.portalVM); 
    }; 
    Manager.prototype.populateTotal = function (result, vm) { 
     console.log(result); 
     console.log(vm); 
     this.portalVM.totalCount = 100000; 
    }; 
    return Manager; 
})(); 

Answer 1

相关线路的位置：

dataTable.take(1).includeTotalCount().read().done(this.populateTotal,this.portalVM); 

您需要捕获的 '这个' 结合因为它将在没有上下文的情况下作为回调被调用。

选项1：

[etc...].done((result, vm) => this.populateTotal(result, vm), this.portalVM); 

选项2：

[etc...].done(this.populateTotal.bind(this), this.portalVM);