javascript - 如何监听 Javascript 中的变量变化？

Question

我一直在使用 Node.js 和 CouchDB。我想要做的是在对象中进行 db 调用。这是我现在正在查看的场景:

var foo = new function(){
   this.bar = null;

   var bar;

   calltoDb( ... , function(){

      // what i want to do: 
      // this.bar = dbResponse.bar;

      bar = dbResponse.bar;      

   });

   this.bar = bar;

}

所有这一切的问题在于 CouchDB 回调是异步的，“this.bar”现在在回调函数的范围内，而不是类。有没有人有任何想法来完成我想要的？我不希望有一个处理程序对象必须对对象进行数据库调用，但现在我真的被它异步的问题难住了。

Answer 1

只需保留对 this 的引用即可:

function Foo() {
   var that = this; // get a reference to the current 'this'
   this.bar = null;

   calltoDb( ... , function(){
      that.bar = dbResponse.bar;
      // closure ftw, 'that' still points to the old 'this'
      // even though the function gets called in a different context than 'Foo'
      // 'that' is still in the scope and can therefore be used
   });
};

// this is the correct way to use the new keyword
var myFoo = new Foo(); // create a new instance of 'Foo' and bind it to 'myFoo'