Adding function to Json Array in AngularJS

I have this JSON object returned from webapi,

[{name:John,val1:10,val2:20,val3:0},
{name:Jane,val1:50,val2:200,val3:0}]

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I store this array in "$scope.dtArray" which is bound to the UI(textboxes) using ng-repeat. before the binding happens I want to assign a function to add values as shown here

this.val3 = function() {return Number(this.val1) + Number(this.val2) };

for each object in the array. SO when ever the user changes the val1 and val2 text boxes, the value changes for val3 automatically.

Following is the UI markup...

<div ng-repeat="cnt in dtArray track by $index">
    <table style="border-style: solid;">
        <tr>
            <td>
                <input type="text" ng-model="cnt.name">
                <input type="text" ng-model="cnt.val1">
                <input type="text" ng-model="cnt.val2">
                <input type="text" ng-model="cnt.val3()">
            </td>
        </tr>
    </table>
</div>

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the function is not getting called in change of value in val1 or val2.

Any help would be appreciated.

Thanks.
LVL 2
rationalJayAsked:
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ambienceCommented:
Try

<input type="text" value="{{val3()}}" >

though it totally does not make sense to use an input for a calculated value. You cannot use ng-model on calculated fields since its not writable.
leakim971PluritechnicianCommented:
test page : https://jsfiddle.net/h24bwg4e/

var myApp = angular.module("myApp", []);
var myCtrl = myApp.controller("myCtrl", ["$scope", function($scope) {
    $scope.dtArray = [
        { name:"John", val1:10, val2:20, val3:0 },
        { name:"Jane", val1:50, val2:200, val3:0 }
    ];
}]);

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Srinivasulu MuppalaLead DeveloperCommented:
Hi replace the line <input type="text" value="{{val3()}}" /> to <input type="text" value="{{cnt.val1 + cnt.val2}}" />

in https://jsfiddle.net/h24bwg4e/
BigRatCommented:
The model in "val3" is actually dtArray[$index].val3, so the function, which is going to change it, must be provided with an index. Angular's ng-model is two way binding, so one just needs to change dtArray and the rest gets updated automatically. ng-repeat adds $index for each element.

We want this to happen when val1 or val2 changes, so we need to trap the ngChange event and call a function which does the calculation :-

$scope.updateVal3(index) {
   $scope.dtArray[index].val3 = $scope.dtArray[index].val1 + $scope.dtArray[index].val2;
}

and then add to the input elements :-

<input type="text" ng-model="cnt.val1" ng-change="updateVal3($index)">
<input type="text" ng-model="cnt.val2" ng-change="updateVal3($index)">

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