javascript - 为什么 Angular 允许动态创建对象？

Question

我不确定标题是否正确传达了我希望澄清的功能。但让我把它放出来。

在 javascript 中我们可以将一个变量实例化为一个空对象:

var person = {};

我们可以轻松地为其设置属性

person.name = "Bob"

但是，我们不能使用属性来分配对象:

person.pet.name = "Bob"
> Uncaught TypeError: Cannot set property 'name' of undefined

在 Angular 你可以。这个适度的代码例如。我有一个 Controller :

angular.module('someModule', [])
  .controller('someController', [
    Callback
  ]

function Callback(){
  this.person = {}
}

然后 View 包含:

<input type="text" data-ng-model='vm.person.pet.name'>

其中 vm 是代表 Controller 的 View 模型。当我记录从输入中获取的结果时，您会得到一个 person 对象，其中有一个 pet 子对象，其属性为 name

什么给了？为什么 Angular 添加此功能？(我假设功能)是否严格是为了灵 active ？

Answer 1

来自docs :

Forgiving

Expression evaluation is forgiving to undefined and null. In JavaScript, evaluating a.b.c throws an exception if a is not an object. While this makes sense for a general purpose language, the expression evaluations are primarily used for data binding, which often look like this:

{{a.b.c}}

It makes more sense to show nothing than to throw an exception if a is undefined (perhaps we are waiting for the server response, and it will become defined soon). If expression evaluation wasn't forgiving we'd have to write bindings that clutter the code, for example: {{((a||{}).b||{}).c}}

Similarly, invoking a function a.b.c() on undefined or null simply returns undefined.

简而言之，html中的表达式<input type="text" data-ng-model='vm.person.pet.name'>不会随时间变化，但实际值为 vm.person.pet.name做。