javascript - angular.js @local scope property coming as undefined if we initialized as null -

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i have made custom angular directive

 <location zipcode="35423" cityname="" statecode=""></location>

and take 

  scope: {                     zipcode: "@",                     cityname: "@",                     statecode: "@"                 },

in contoller of directive :

 controller: function ($scope, $filter) { $scope.zipcode = "35423" // here values $scope.cityname = undefined // ?? why? $scope.statecode= undefined // ?? why? }

i want $scope.cityname = ""

in reality using mvc application

zipcode="@zipcode" cityname="@city" statecode="@statecode"

and might possible city null

you can set value of scope properties "" if they're undefined so: $scope.cityname = $scope.cityname || "";.

i don't understand why though, since "" , undefined both evaluate false.


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