ng-model值字符串转数值型（convertToNumber directive）

<select ng-model="model.id" convert-to-number>
  <option value="0">Zero</option>
  <option value="1">One</option>
  <option value="2">Two</option>
</select>
{{ model }}

angular.module('nonStringSelect', [])
.run(function($rootScope) {
  $rootScope.model = { id: 2 };
})

.directive('convertToNumber', function() {
  return {
    require: 'ngModel',
    link: function(scope, element, attrs, ngModel) {

//format text from the user (view to model)

ngModel.$parsers.push(function(val) { return parseInt(val, 10); }); 

//format text going to user (model to view)

ngModel.$formatters.push(function(val) { return '' + val; }); } }; });

Formatters Definition

Array of functions to execute, as a pipeline, whenever the model value changes. Each function is called, in turn, passing the value through to the next. Used to format / convert values for display in the control and validation.

Parsers Definition

Array of functions to execute, as a pipeline, whenever the control reads value from the DOM. Each function is called, in turn, passing the value through to the next. Used to sanitize / convert the value as well as validation. For validation, the parsers should update the validity state using $setValidity(), and return undefined for invalid values.

To summarize:

• Formatters change how model values will appear in the view.
• Parsers change how view values will be saved in the model.