How to count Angular Watchers on Page? - angularjs

Question

How do I accurately count the number of watchers on a page?
I found a few different articles on how to do it, but they all give me different counts, so I'm struggling to find which is the correct way.
There is a StackOverflow here with the following code:
(function () {
var root = angular.element(document.getElementsByTagName('body'));
var watchers = [];
var f = function (element) {
angular.forEach(['$scope', '$isolateScope'], function (scopeProperty) {
if (element.data() && element.data().hasOwnProperty(scopeProperty)) {
angular.forEach(element.data()[scopeProperty].$$watchers, function (watcher) {
watchers.push(watcher);
});
}
});
angular.forEach(element.children(), function (childElement) {
f(angular.element(childElement));
});
};
f(root);
// Remove duplicate watchers
var watchersWithoutDuplicates = [];
angular.forEach(watchers, function(item) {
if(watchersWithoutDuplicates.indexOf(item) < 0) {
watchersWithoutDuplicates.push(item);
}
});
console.log(watchersWithoutDuplicates.length);
})();
When I test it on the Angularjs.org homepage, it gives me 132 watchers.
I then found a Medium post here, with the following code:
function getWatchers(root) {
root = angular.element(root || document.documentElement);
var watcherCount = 0;
function getElemWatchers(element) {
var isolateWatchers = getWatchersFromScope(element.data().$isolateScope);
var scopeWatchers = getWatchersFromScope(element.data().$scope);
var watchers = scopeWatchers.concat(isolateWatchers);
angular.forEach(element.children(), function (childElement) {
watchers = watchers.concat(getElemWatchers(angular.element(childElement)));
});
return watchers;
}
function getWatchersFromScope(scope) {
if (scope) {
return scope.$$watchers || [];
} else {
return [];
}
}
return getElemWatchers(root);
}
getWatchers().length
Testing this on Angularjs.org homepage returns 152 watchers.
Using simply angular.element('body').scope().$$watchersCount returns 80.
I understand that the SO code removes duplicates, is it removing duplicates that are watching the same expression (so there will only be one watcher listed for an expression like !visible), or it's removing duplicate watcher objects?
Update:
I realize the discrepancy is from duplicates. But, do duplicate watchers affect performance?

Answer 1

This script will help you identify how many watchers are there on your
page
just paste the below script on your browser's console and it will tell you the watcher count on your page
function getWatchers(root) {
root = angular.element(root || document.documentElement);
var watcherCount = 0;
function getElemWatchers(element) {
var isolateWatchers = getWatchersFromScope(element.data().$isolateScope);
var scopeWatchers = getWatchersFromScope(element.data().$scope);
var watchers = scopeWatchers.concat(isolateWatchers);
angular.forEach(element.children(), function (childElement) {
watchers = watchers.concat(getElemWatchers(angular.element(childElement)));
});
return watchers;
}
function getWatchersFromScope(scope) {
if (scope) {
return scope.$$watchers || [];
} else {
return [];
}
}
return getElemWatchers(root);
}
getWatchers().length