ng-change get new value and original value

Question

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.

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>

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}}')">

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.

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