为了在 javascript(不仅仅是 angularjs)中有 2 路绑定，我们必须传递一个对象(这是由 javascript 的评估策略引起的 - 可以阅读更多关于这里 https://en.wikipedia.org/wiki/Evaluation_strategy#Call_by_sharing).基本上发生的事情是，当我们传递一个原始变量时，它是通过值传递并重新创建的，而不是通过引用传递.只有对象通过引用传递.

In order to have 2 way binding in javascript (not just angularjs), we have to pass an object (this is caused by javascript's evaluation strategy - can read more about it here https://en.wikipedia.org/wiki/Evaluation_strategy#Call_by_sharing). basically what is happening is that when we pass a primitive variable, its been passed by value and re-created, instead of been passed by reference. only objects are passed by reference.

所以这个问题可以通过传递变量的父对象来解决，例如:

So this issue can be solved by passing the variable's parent object, for example:

<custom-directive ng-model-name="variable" ng-model-parent="parentObj"></custom-directive>

然后，将指令中的对象修改如下:

and then, modifying in object in the directive as following:

parentObj[variable] = "whatever";

这样，我们将保持变量与 parentObj 之间的连接.

this way, we will keep the connection between the variable to the parentObj.

另一种选择是通过父对象传递模型，例如:

another option would be passing the model with the parent obj, for example:

<custom-directive ng-model="parentObj.variable"></custom-directive>

点是这个例子的重要组成部分.它实际上是 angular 的***实践，始终使用 parentObj-dot-property 传递变量.

the dot is an important part of this example. its actually a best practice by angular to always pass variables with the parentObj-dot-property.

有关其他信息，angularjs 实际上有关于它的文档 https://github.com/angular/angular.js/wiki/Understanding-Scopes

for additional information, angularjs actually has a documentation about it https://github.com/angular/angular.js/wiki/Understanding-Scopes