Angular4真的是2向数据绑定吗？

Question

What I have learned of Angular2/4/5/6 is that due to [(ngModel)] the 2-way data binding is possible in it -- Just like it happend in Angular1 via $scope.

Now, I came across this website which clearly states that 2-Way data binding is not possible in Angular4. I am highly confused. Can someone really clarify that -- whether 2-Way data binding is possible or Not in Angular 2/4/5/6?

Link: https://dzone.com/articles/understanding-output-and-eventemitter-in-angular

Answer 1

whether 2-Way data binding is possible or Not in Angular 2/4/5/6?

Nope, it is not [(ngModel)] is not two-way data binding. It's just a syntactic sugar for a simultaneous event binding and property binding.

To Explore more on this

1. Do you really know what unidirectional data flow means in Angular

2. Change Detection Reinvented Victor Savkin
3. TWO-WAY DATA BINDING IN ANGULAR

Answer 2

Angular is a javascript framework and javascript has limitations that does not allow real two-way databinding.

Indeed, the first way (template to variable) is made possible thanks to native javascript API that allows to listen to events on input fields, but there is not such thing as events emitted when a variable changes, so the other way is not feasible with the javascript API.

Here comes the detection change , made possible by Zone.js, Angular "listens" to your code and triggers a change detection on these three types of events:

• User event on page (click, submit, blur, etc...)
• XMLHttpRequest has ended
• A timer ( setTimeout or setInterval ) triggered some function

The change detection updates the template with every bound variable.

That's how the two-way databinding virtually exists.

And by the way [(ngModel)] is syntaxic sugar for [ngModel]="variable" (ngModelChange)="variable = $event" : these are the two ways