Scope function calling on DOM change(two-way data binding) angularjs - javascript

<!DOCTYPE html>
<html data-ng-app="app">
<head>
<title></title>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.5.6/angular.min.js"></script>
</head>
<body data-ng-controller="SimpleController">
<script>
var app = angular.module('app', []);
app.controller('SimpleController', SimpleController);
function SimpleController($scope) {
$scope.isNumberA = function(val) {
console.log('called');
if (val == 2) return true;
}
}
</script>
<input type="checkbox" ng-model="switcher" />
<h1 ng-if="isNumberA(10)">isNumber</h1>
</body>
</html>
In the above code first time, isNumberA calling because of ng-if="isNumberA(10)" but I don't know why it is calling another time. Check console, it prints two times on DOM render in brower. After that when I click on check box again it calling the function. Why this method calling on check box click? I didn't called it. Is this the two-way binding? And also if I remove the <h1 ng-if="isNumberA(10)"></h1>, it is not calling. What is happening here?

You have used a function call rather then a variable for condition (ng-if).
Angular watch every scope variable used in view, but when you use a function call, it can't decided which variable or event will effect this function return value, so Angular run such function on every digest cycle.
You should call this function in ng-init and store the return value of this function in a variable, and use that variable in ng-if.
$scope.isNumberA = function(val) {
console.log('called');
if (val == 2){
$scope.showIfBlock = true;
} else {
$scope.showIfBlock = false;
}
}
<span ng-init="isNumberA(10)"></sapn>
<h1 ng-if="showIfBlock">isNumber</h1>

ng-if will evaluate its expression when digest cycle runs, basically you shouldn't make an function call from ng-if expression.
DEMO
<!DOCTYPE html>
<html data-ng-app="app">
<head>
<title></title>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.5.6/angular.min.js"></script>
</head>
<body data-ng-controller="SimpleController">
<script>
var app = angular.module('app', []);
app.controller('SimpleController', SimpleController);
function SimpleController($scope) {
$scope.isNumberA = function(val) {
console.log('called');
if (val == 2) $scope.block = true;
$scope.block = false;
}
}
</script>
<input type="checkbox" ng-model="switcher" />
<span ng-init="isNumberA(10)"></sapn>
<h1 ng-if="block">isNumber</h1>
</body>
</html>
Read More here
ng-if being called more times than it should

Related

Function prints entirely

Extremely new to AngularJs and trying to figure out why my function prints out entirely as follows.
Hello function () { return (this.sal) * 12; }
Here is my code.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.6.4/angular.min.js"></script>
<script type="text/javascript">
var app=angular.module("sample",[]);
app.controller("emp",function($scope){
$scope.Name="Jag";
$scope.sal="4500"
$scope.getAnnualSal = function()
{
return (this.sal) * 12;
}
});
</script>
</head>
<body ng-app="sample">
<div ng-controller="emp">
Hello {{getAnnualSal}}
</div>
</body>
</html>
Try this, it's a function not a variable:
Hello {{getAnnualSal()}}
It is evaluating getAnnualSal as a property in the scope. If you want to execute it as a function in the scope, add ()
{{getAnnualSal()}}
As already stated, you should be using as a function with ().
I wanted to also mention that your function should be using $scope.sal in Angular versus this.sal.
$scope.getAnnualSal = function () {
return $scope.sal * 12;
}
And usage:
Hello {{getAnnualSal()}}

Angularjs: why there are 3 watchers for 1 binding?

Please take a look at the screenshot given below
As you can see in the screenshot above there are #3 watchers for a single binding.
Can anyone please elaborate why is it so?
P.S: I am using AngularJS Batarang for checking the performance.
var app = angular.module('app', []);
app.controller('appCtrl', function ($scope, $timeout) {
$scope.name = 'vikas bansal';
})
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.5.5/angular.min.js"></script>
<script src="app.js"></script>
</head>
<body>
<div ng-app="app" ng-controller="appCtrl">
{{name}}
</div>
</body>
</html>
I think Angular Batarang has a wrong counter of watchers. I checked with few different sources, and all except AngularJS Batarang show me single watcher on your code. Check out this question with function:
(function () {
var root = angular.element(document.getElementsByTagName('body'));
var watchers = [];
var f = function (element) {
angular.forEach(['$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);
})();
And you can check Watchers extension for chrome. Both show 1 watcher.

Why printing multiple times on calling a function - AngularJS

I am calling a function from the controller scope, but in the console the values are printed three times. Why is this happening?
SOURCE
<!DOCTYPE html>
<html ng-app="myModule" >
<head>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.3.15/angular.min.js"></script>
</head>
<body ng-init="priceList='promo03,promo04'">
<div ng-controller="PricingController" >
{{splitArray()}}
</div>
<script>
var myModule = angular.module('myModule',[]);
myModule.controller('PricingController',['$scope', function($scope){
$scope.priceString = $scope.priceList;
$scope.array = [];
$scope.splitArray= function(){
console.log($scope.priceString);
$scope.array = $scope.priceString.split(",");
console.log($scope.array[0]);
console.log($scope.array[1]);
};
}]);
</script>
</body>
</html>
CONSOLE OUTPUT
promo03,promo04
promo03
promo04
promo03,promo04
promo03
promo04
promo03,promo04
promo03
promo04
Expected Output
promo03,promo04
promo03
promo04
This is called for every digest loop of Angular.
If you keep your program running, you'll have even more logs.
To prevent it, call your function INTO your controller, not into a binded value into your html.
For instance :
$scope.splitArray= function(){
console.log($scope.priceString);
$scope.array = $scope.priceString.split(",");
console.log($scope.array[0]);
console.log($scope.array[1]);
};
$scope.splitArray();

ANgularJS binding element to function output with ng-change

AngularJS beginner here. Writiung a simple page to learn. All it does is take a user input and then apply an operation to it (*10) and display that in the page. I have no idea why this is not working, no value for {{funding.needed}} is ever displayed....any ideas?
<html ng-app>
<head>
<title>Learning</title>
</head>
<!--View - user input to collect a value and then apply logic to it-->
<div>
<form ng-controller="StartUpController">
Starting: <input ng-change="computeNeeded()"
ng-model="funding.startingEstimate">
Recommendation: {{funding.needed}}
</form>
</div>
<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.0.8/angular.min.js"></script>
<script>
//startup controller to intiialize variable and computeNeeded function to apply logic
function StartUpController($scope) {
$scope.funding = {startingEstimate: 0};
};
$scope.computeNeeded = function(){
$scope.funding.needed = $scope.funding.startingEstimate * 10;
};
</script>
</body>
</html>
The computeNeeded function needs to be included in the controller so it has access to the $scope object:
<script>
//startup controller to intiialize variable and computeNeeded function to apply logic
function StartUpController($scope) {
$scope.funding = {startingEstimate: 0};
$scope.computeNeeded = function(){
$scope.funding.needed = $scope.funding.startingEstimate * 10;
};
};
</script>

infdig Infinite $digest Loop

I'm learning AngularJs but I cant make it works.
I read about the digest cycle but it is not clear for me.
It's obvious that this code fails because enter in a infinite loop, but I dont know how to fix it.
Could someone help me?
<!DOCTYPE html>
<html lang="eng" ng-app="test">
<head>
<title>Learning Angular</title>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.9/angular.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.9/angular-route.js"></script>
<script type="text/javascript">
var app = angular.module('test', ['ngRoute']);
app.factory('visitCounterService', function () {
var counterService = function() {
var _count = 1;
var counter = function() { return _count++; };
return { counter: counter }
}();
return counterService;
});
app.service('homeModel', ['visitCounterService', function(visitCounterService){
this.getTitle = function() {
var n = visitCounterService.counter();
return "Welcome to this awesome demo. You are the visitor n° " + n;
};
}]);
app.controller('homeController', ['$scope', 'homeModel', function($scope, homeModel) {
$scope.home = homeModel;
}]);
</script>
</head>
<body ng-controller="homeController">
<h3>{{home.getTitle()}}</h3>
</body>
</html>
Thanks in advice!!!
Angular registers an implicit $watch on the home.getTitle() expression. This expression will get called at least twice because angular wants to check if the model has stabilized.
Your code returns a different string everytime home.getTitle() is called so angular continues digesting until it reaches the max digest cycles limit.
Try:
$scope.homeTitle = homeModel.getTitle();
and
<h3>{{homeTitle}}</h3>

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