ng-init仅当value为null / undefined时

Question

Is there a way to use ng-init so that it is only run if the value in ng-model is null or undefined?

I have this input

<input ng-model="entry.Value.Currency" type="text" placeholder="Currency">

I would like the "Currency" value to be set to 'USD' if entry.Value.Currency == null . Note that it could contain a completly different value like 'EUR' in which case I want the code to do nothing.

As it is now whatever I type in the field just gets deleted, which I think is because .Currency does not exist / is undefined. If it helps the value of entry.Value is always guaranteed to exist / not be null.

Tried adding ng-init="entry.Value.Currency ='USD'" to the input field but that did not seem to do anything at all.

I would like to accomplish this without initializing the Currency variable in javascript as inputs can be added dynamically and what values they add to entry.Value may differ. The only thing I know for each input control is that entry.Value = {};

Answer 1

What would suit you best is a directive that uses the ngModelController

I've written one that should do what you want, the code for it is

myApp.directive('currencyInit', function() {
  return {
    restrict: "A",
    require: 'ngModel',
    link: function(scope, element, attrs, ngModel) {
      if (!ngModel) return;

      ngModel.$render = function() {
        if (ngModel.$modelValue == undefined || ngModel.$modelValue == null) {
          ngModel.$setViewValue('USD');
        }
        element.val(ngModel.$viewValue);
      }  
    }
  }
});

And to see it in action you can look at this JSFiddle

PS Sorry I took so long to write it I went out for lunch 😀

Answer 2

您可以使用ng-attr-placeholder="{{!entry.Value.currency?'USD':'something'}}"