如何更改 <select>从控制器使用angularJS的值？

Question

I am having a select element with 1-10 options as:

<select id="selVal" ng-model="product.quantity" ng-options="o as o for o in quantityValues" ng-change="updateDelta(product.quantity, {{product.quantity}}, product.selected_size.qty_avail)"></select>

while on controller side looks like:

$scope.quantityValues = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

prerequisite: initially product.quantity < product.selected_size.qty_avail

what i want to do that when I try to select other option such that if value corresponding this new option is greater than the available quantity than update and display last selected option ie one where selected option value was less than available quantity:

$scope.updateDelta = function(currentSelectedVal, prevSelectedVal, selectedProductAvailQty) {

    if(product.quantity > selectedProductAvailQty) {

    //than 

    #scope.product.quantity = prevSelectedVal;//still in product.quantity in view previous value is not displayed

    }
}

example: if available_quantity=4; previous selected product quantity=2; current selected product quantity=8

current o/pi am getting: still 8 is displayed in select html tag

expected: display previous selected product quantity ie display 2

Answer 1

Remember the old value in your controller (I placed it into the product variable).

HTML:

<select ng-model="ctrl.product.quantity" ng-change="ctrl.updateDelta(ctrl.product.quantity)" ng-options="o as o for o in ctrl.quantityValues"></select>

Controller:

vm.product = {
    quantity: 4,
    qty_avail: 6,
    prevSelected: this.quantity
};

vm.updateDelta = function(newVal) {
    if (newVal > vm.product.qty_avail) {
       vm.product.quantity = vm.product.prevSelected;
    }
    else
    {
    vm.product.prevSelected = newVal;
    }
};

Example in Plnkr