why is two-way binding undefined in angularjs directive link function?

Question

I am trying to send data from controller to directive , but i am getting undefined why ?

here is my code https://plnkr.co/edit/0gtFynDdvyY0sWqKGI2l?p=preview

I do the following steps

  <div img-upload="" previewData="data" method="POST" 
       url="webfreaks.in/dummyService">
  </div>

previewData="data" send data in directive in controller I defined like this

$scope.data =['sds']

but when i am trying to get its value in the directive . I am getting undefined undefined

why ?

link : function(scope,elem,attrs){
    var formData = new FormData();
    console.log(scope.previewData)

scope

scope : {
    url : "@",
    method : "@",
    previewData:'=',
},

Answer 1

模板中的PreviewData必须像这样的“预览数据”（使用kebab-case进行模板中的绑定）：

<div img-upload="" preview-data="data" method="POST" url="webfreaks.in/dummyService"></div>