Dan Wahlin Dan Wahlin - 2 months ago 9
AngularJS Question

Function Called Multiple Times in AngularJS Repeat Section

I'm running into an issue where I want to bind to the output of a function inside of an ng-repeat loop. I'm finding that the function is being called twice per item rather than once as I'd expect. Here's the ng-repeat section (notice the calcRowTotal() call at the end):

<tr ng-repeat="row in timesheetRows">
<td>
<select ng-model="row.categoryID">
<option ng-repeat="category in categories" value="{{category.id}}">
{{category.title}}
</option>
</select>
</td>
<td ng-repeat="day in row.dayValues">
<input type="text" ng-model="day.hours" />
</td>
<td>{{calcRowTotal($index, row)}}</td>
</tr>


The calcRowTotal() function is shown next:

$scope.calcRowTotal = function (index, row) {
console.log('calcRowTotal - Index: ' + index);
var total = 0;
for (var i = 0; i < row.dayValues.length; i++) {
var num = parseFloat(row.dayValues[i].hours);
if (isNaN(num)) {
num = 0;
//this.dayValues[i].hours = 0;
}
total += num;
}
//updateDayTotals();
return total;
}


An example of one of the items being iterated through is shown next:

{
categoryID: 2,
dayValues: [
{ day: $scope.days[0], hours: 5 },
{ day: $scope.days[1], hours: 0 },
{ day: $scope.days[2], hours: 3 },
{ day: $scope.days[3], hours: 0 },
{ day: $scope.days[4], hours: 2 },
{ day: $scope.days[5], hours: 5 },
{ day: $scope.days[6], hours: 8 }
]
}


I'm seeing the following in the console (two items are currently in the collection I'm looping through):

calcRowTotal - Index: 0
calcRowTotal - Index: 1
calcRowTotal - Index: 0
calcRowTotal - Index: 1


I could certainly make a "rowTotal" property but would prefer to bind to "live" data provided by the function shown above. Hopefully the duplication is something simple I'm missing so I appreciate any feedback on why I'm seeing the duplication. As a side note, as data in one of the textboxes changes I need to update the row totals as well so it may be I need a different approach. Interested in understanding this particular situation first though....definitely don't want the duplication because there could be a lot of rows potentially.

Here's an example: http://jsfiddle.net/dwahlin/Y7XbY/2/

Answer

It's because you're binding to a function expression here:

<td>{{calcRowTotal($index, row)}}</td>

What that does it force that function to be reevaluated on every item, on every digest. What you'll want to do to prevent that is pre-calculate that value and put it in your array to begin with.

One way to do that is to set up a watch on your array:

$scope.$watch('timesheetRows', function(rows) {
   for(var i = 0; i < value.length; i++) {
     var row = rows[i];
     row.rowTotal = $scope.calcRowTotal(row, i);
   }
}, true);

Then all you have to do is bind to that new value:

<td>{{row.rowTotal}}</td>