javascript - 闭包问题和别处定义的方法

Question

我是 Javascript 的新手，所以我可能没有使用准确的术语。

假设我这样定义一个对象字面量。

var myObj = { 
   someMethod:function() {
      //can we have access to "someValue" via closure?
      alert(someValue);
   }
}

然后我们像这样将函数分配给另一个对象。

var myOtherObject  = {
   someOtherMethod:function() {
      var someValue = 'Hello World';

      //If we did this, then the function would have access to "someValue"
      this.aMethod = function() {
        alert(someValue);
      }

      //This does not work for "someMethod" to have access to "someValue"
      //this.someMethod = myObj.someMethod;

      //This does work, however I would like to avoid the use of eval()
      this.someMethod = eval("("+myObj.someMethod.toString()+")");

   }
}

是否可以在不使用上述 eval() 的情况下让 myOtherObject.someMethod() 工作？

Answer 1

someValue 是 someOtherMethod 的本地值，myObj.someMethod() 无法以任何方式访问。有两种解决方案:

a) 将 someValue 作为参数传递给第一个方法:

var myObj = { 
   someMethod:function(someValue) {
      alert(someValue);
   }
}
var myOtherObject  = {
   someOtherMethod:function() {
      var someValue = 'Hello World';
      // The next line illustrates the 'closure' concept
      // since someValue will exist in this newly created function
      this.someMethod = function () { myObj.someMethod(someValue); };
   }
}
myOtherObject.someOtherMethod();
myOtherObject.someMethod();

b) 将 someValue 存储为对象本身的成员，而不是局部变量:

var myObj = { 
   someMethod:function() {
      alert(this.someValue);
   }
}
var myOtherObject  = {
   someOtherMethod:function() {
      this.someValue = 'Hello World';
      this.someMethod = myObj.someMethod;
   }
}
myOtherObject.someOtherMethod();
// 'this' in someMethod will here refer to the new myOtherObject
myOtherObject.someMethod();