Understanding the ngRepeat 'track by' expression

Question

I\'m having difficulties understanding how the track by expression of ng-repeat in angularjs works. The documentation is very scarce: http://docs.angularjs.

Answer 1

You can track by $index if your data source has duplicate identifiers

e.g.: $scope.dataSource: [{id:1,name:'one'}, {id:1,name:'one too'}, {id:2,name:'two'}]

You can't iterate this collection while using 'id' as identifier (duplicate id:1).

WON'T WORK:

  // something with item ...

but you can, if using track by $index:

  // something with item ...