ng-change get new value and original value - angularjs

Question

I'm using ng-options to select values from a pulldown. I'd like to be able to compare the old value to the new value. ng-change works well for grabbing the new value of the pull down, but how can I get both the new value and the original value?
<select ng-change="updateValue(user)" ng-model="user.id" ng-options="user.id as user.name for user in users"></select>
For instance, let's say I wanted the controller to log, "Your former user.name was BILL, your current user name is PHILLIPE."

Answer 1

With an angular {{expression}} you can add the old user or user.id value to the ng-change attribute as a literal string:
<select ng-change="updateValue(user, '{{user.id}}')"
ng-model="user.id" ng-options="user.id as user.name for user in users">
</select>
On ngChange, the 1st argument to updateValue will be the new user value, the 2nd argument will be the literal that was formed when the select-tag was last updated by angular, with the old user.id value.

Answer 2

Also you can use
<select ng-change="updateValue(user, oldValue)"
ng-init="oldValue=0"
ng-focus="oldValue=user.id"
ng-model="user.id" ng-options="user.id as user.name for user in users">
</select>

Answer 3

You can use something like ng-change=someMethod({{user.id}}).
By keeping your value in side {{expression}} it will evaluate expression in-line and gives you current value(value before ng-change method is called).
<select ng-model="selectedValue" ng-change="change(selectedValue, '{{selectedValue}}')">

Answer 4

Just keep a currentValue variable in your controller that you update on every change. You can then compare that to the new value every time before you update it.'
The idea of using a watch is good as well, but I think a simple variable is the simplest and most logical solution.

Answer 5

You can use a scope watch:
$scope.$watch('user', function(newValue, oldValue) {
// access new and old value here
console.log("Your former user.name was "+oldValue.name+", you're current user name is "+newValue.name+".");
});
https://docs.angularjs.org/api/ng/type/$rootScope.Scope#$watch

Answer 6

You could use a watch instead, because that has the old and new value, but then you're adding to the digest cycle.
I'd just keep a second variable in the controller and set that.

Answer 7

You can always do:
... ng-model="file.PLIK_STATUS" ng-change="file.PLIK_STATUS = setFileStatus(file.PLIK_ID,file.PLIK_STATUS,'{{file.PLIK_STATUS}}')" ...
and in controller:
$scope.setFileStatus = function (plik_id, new_status, old_status) {
var answer = confirm('Czy na pewno zmienić status dla pliku ?');
if (answer) {
podasysService.setFileStatus(plik_id, new_status).then(function (result) {
return new_status;
});
}else{
return old_status;
}
};