Assign value to a variable in a controller and do not modify the value of the $Scope variable

Question

I wonder why when I assign the value to a variable within a controller coming from a $Scope variable and change the value of that variable, the value of the $Scope variable is also changed. For example:

$scope.viagem.valorFrete = 1.500,20; 
var viagemPersistencia.valorFrete = $scope.viagem.valorFrete.replace('.','').replace(',','.');

Afterward var viagemPersistencia.valorFrete= 1500.20 and the value of $scope.viagem.valorFrete equal to that 1500.20 when it might be 1,500.20 in the view, I would like the value of $scope.viagem.valorFrete did not change.

Edited The request follows part of my code not to extend.

Part of html:

<input id="freteviagem" maxlength="9" type="text" name="freteviagem" ng-model="viagem.valorFrete">
      <div id="btn-salvar" style="text-align:right;">
      <button type="button" class="btn btn-primary" ng-click="salvar(viagem)">
          <span class="fonte-viagem">Salvar</span>
      </button>
</div>

Controller:

  $scope.salvar = function(viagem) {
     var viagemPersistencia = viagem;
     viagemPersistencia.valorFrete = viagemPersistencia.valorFrete === 
     undefined || viagemPersistencia.valorFrete === null ? null 
     (viagemPersistencia.valorFrete + "")
     .replace('.','').replace(',','.');
    //VALOR $scope.viagem.valorFrete é o mesmo de viagemPersistencia.valorFrete neste momento 
  }

Answer 1

In Javascript variables are passed by reference, then if the variable viagemPersistencia the saved copy of viagem will also be impacted.

Making a reference copy (angular.copy), a new object is created with no link to the original. So the idea would be to ensure that the content of viagem will not change after changing viagemPersistencia.

Try to use angular copy.

var viagemPersistencia = angular.copy(viagem);