The method by which AngularJS identifies the appropriate property within a return value

Question

The method by which AngularJS identifies the appropriate property within a return value

In Angular, watchers are utilized to identify property changes and trigger a listener function. An example of a watcher declaration is shown below:

$scope.food = "chicken";
scope.$watch(
    function() { return food; },
    function(newValue, oldValue) {
        if ( newValue !== oldValue ) {
            // Only increment the counter if the value changed
            scope.foodCounter = scope.foodCounter + 1; }
    }
);

The first parameter is simply a function with a return value. However, how does Angular recognize that this return value corresponds to the 'food' property? How is this mapping achieved?

javascript angularjs

Answer 1

Answer №1

Angular takes your function, saves the output.
He checks for any changes by running the function again and comparing the new value with the old one.

Answer 2

Angular takes your function, saves the output.
He checks for any changes by running the function again and comparing the new value with the old one.

Answer 3

Answer №2

It is important to specify what you want to monitor for changes and then access the old and new values accordingly.

$scope.drink = "water";
$scope.$watch(function(scope) { return scope.drink  },
       function(newDrink, oldDrink) {
                 //Your custom code goes here. It will trigger whenever the drink value changes
        }
 });

Answer 4

It is important to specify what you want to monitor for changes and then access the old and new values accordingly.

$scope.drink = "water";
$scope.$watch(function(scope) { return scope.drink  },
       function(newDrink, oldDrink) {
                 //Your custom code goes here. It will trigger whenever the drink value changes
        }
 });

Answer 5

Answer №3

Let's examine this code snippet:

scope.$watch('food', function(newValue, oldValue) {
});

This is equivalent to:

scope.$watch(function() { return food; }, function(newValue, oldValue) {
});

Essentially, the function returns the value of 'food' being watched and it is executed during each iteration of the $digest loop, causing your counter to increase.

Answer 6

Let's examine this code snippet:

scope.$watch('food', function(newValue, oldValue) {
});

This is equivalent to:

scope.$watch(function() { return food; }, function(newValue, oldValue) {
});

Essentially, the function returns the value of 'food' being watched and it is executed during each iteration of the $digest loop, causing your counter to increase.

The method by which AngularJS identifies the appropriate property within a return value

Answer №1

Answer №2

Answer №3

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