javascript – AngularJs为什么更新属性比更新varibale更好？

2019年8月4日 173次阅读

来自“ng-book”,它说：

Due to the nature of JavaScript itself and how it passes by value vs. reference, it’s considered a best-practice in Angular to bind references in the views by an attribute on an object, rather than the raw object itself.

…..

In this case, rather than updating the $scope.clock every second, we can update the clock.now property. With this optimization, we can….

我不知道为什么,因为“JavaScript：The Definitive Guide”说：

Is there really any fundamental difference between the variable i and
the property i of an object o? The answer is no. Variables in
JavaScript are fundamentally the same as object properties.

在这本书中：

$scope.time = { now: new Date()}

比…更好

$socpe.time = new Date();

最佳答案 考虑这个示例HTML：

<div ng-app>
    <div ng-controller="MyController">
        <div>{{rawObj}}</div>
        <div>{{obj.prop}}</div>
        <div ng-if="isShown">
            <input ng-model="rawObj" />
            <input ng-model="obj.prop" />
            <span>{{readOnly}}</span>
        </div>
    </div>
</div>

在js中你有一个控制器：

 function MyController($scope){
    $scope.rawObj = "raw value";
    $scope.obj = {
        prop: "property of object"
    }
    $scope.readOnly = "read only";
    $scope.isShown = true;
 }

如果您使用ng-model =“rawObj”开始输入输入,则不会修改MyController中$scope作为属性的rawObj,但会在ng-if的范围内创建新属性rawObj.如果我没有在包装div上放置ng-if指令,一切都会正常工作.当您在输入和具有ng-controller(在这种情况下)的元素之间的元素上有一个指令时,会发生这种情况,该控制创建了自己的非隔离范围.许多指令都是这样的：ng-if或ng-repeat.

如果在ng-model中引用对象的属性,它将“查找”父作用域中的对象并找到适当的作用域.

在小提琴上查看：http://jsfiddle.net/VC5WK/

这是由于javascript中的原型继承如何像以前的answears状态一样工作.

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