$watch’ing for data changes in an Angular directive

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You need to enable deep object dirty checking.
By default angular only checks the reference of the top level variable that you watch.

App.directive('d3Visualization', function() {
    return {
        restrict: 'E',
        scope: {
            val: '='
        },
        link: function(scope, element, attrs) {
            scope.$watch('val', function(newValue, oldValue) {
                if (newValue)
                    console.log("I see a data change!");
            }, true);
        }
    }
});

see Scope. The third parameter of the $watch function enables deep dirty checking if it’s set to true.

Take note that deep dirty checking is expensive. So if you just need to watch the children array instead of the whole data variable the watch the variable directly.

scope.$watch('val.children', function(newValue, oldValue) {}, true);

version 1.2.x introduced $watchCollection

Shallow watches the properties of an object and fires whenever any of the properties change (for arrays, this implies watching the array items; for object maps, this implies watching the properties)

scope.$watchCollection('val.children', function(newValue, oldValue) {});

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