Get object property which fired the $watch

Question

When you're using a $watch method (with equality by value). Is there a way to see which object property was changed?

e.g.

/** * Save state of button: Cancelled */ $scope.$watch('buttons.cancelled', function(newValue, oldValue) { if(newValue != oldValue && newValue !== undefined) { privates.viewState.buttons.cancelled = $scope.buttons.cancelled; } }); /** * Save state of button: Booked */ $scope.$watch('buttons.booked', function(newValue, oldValue) { if(newValue != oldValue && newValue !== undefined) { privates.viewState.buttons.booked = $scope.buttons.booked; } });

Turned into;

 $scope.$watch('buttons', function(newValue, oldValue) { if(newValue != oldValue && newValue !== undefined) { //Is there a way to know which button triggered this watch? } }, true);

Well, you have the newValue and oldValue so you got to do the comparison yourself (if(newValue.booked !== oldValue.booked){'booked changed!'}). — Stewie
– Stewie, Commented Jan 14, 2014 at 15:19

Community · Accepted Answer · 2017-05-23 11:57:38Z

Here is an example.

I would also like to see an angular built-in feature but as for now You need to do that manually

I put the buttons inside array of objects rather than in hash keys because:

Hash keys are harder to iterate and transform.
I use ng-model (Difficulty with ng-model, ng-repeat, and inputs)

$watch is invoked with new Value and old Value, just compare them :

$scope.buttons = [ { name: 'cancelled', checked: false}, { name: 'booked', checked: false}, { name: 'something', checked: false} ]; $scope.$watch('buttons',function(newVal,oldVal){ oldVal = oldVal.reduce(function(p,k){ p[k.name] = k.checked; return p;},{}); var changed = newVal.filter(function(k){ return oldVal[k.name] !== k.checked; }); changed = changed.reduce(function(p,k){ p[k.name] = k.checked; return p;},{}); $scope.changed = changed; },true);

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Get object property which fired the $watch

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$watch is invoked with new Value and old Value, just compare them :

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$watch is invoked with new Value and old Value, just compare them :

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