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In AngularJs which way is better while using ng-if, is to perform the condition in the template or call a function that return true or false

<!-- template.html -->
<div ng-if="items.length > 0">
<!-- content -->
</div>
vs
<!-- template.html -->
<div ng-if="$ctrt.hasItems()">
<!-- content -->
</div>
<!-- controller.js -->
$ctrt.hasItems = (itmesList) => {
return items.length > 0
};
which way is better, doing the evaluation in javascript or in the HTML template?

The second example will run the function multiple times. I think it's because angular doesn't know if any $scope value has changed during each digest cycle. So the function will get executed for each digest cycles. In your case, it will get executed when the ng-if conditions become true.
Here is a demo that would replicate this behaviour:
var app = angular.module('myApp', []);
app.controller('myCtrl', function($scope) {
$scope.items = [1, 2, 3];
var x = 0;
$scope.hasItems = function() {
x++;
console.log("execution", x);
return $scope.items.length > 0;
}
});
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.6.4/angular.min.js"></script>
<div ng-app="myApp" ng-controller="myCtrl">
Test:
<div ng-if="hasItems()">Has items</div>
</div>
It's always better to populate the variable in the controller, rather than check for that variable's value with any get method / function. So use your first case, where you check it directly.

Is there any way to use two ng-app's like parent and clild app in AngularJs?

HTML
chech out the below sample html, I require something like this.
<div id="parentApp" ng-app="parentApp" ng-cloak="" ng-controller="mainController">
<div id="someContent">
{{$scope.parentName}}
***some parent app actions***
</div>
<div id="childApp" ng-app="childApp">
<div id="someContent" ng-controller="secondController">
{{$scope.childName}}
***some child app actions***
</div>
</div>
</div>
Script
2 simple app and controllers for better understanding purpose.
var parentApp = angular.module('parentApp', []);
parentApp.controller('mainController', function($scope, $http) {
$scope.parentName = 'Parent!!'
});
var childApp = angular.module('childApp', []);
childApp.controller('secondController', function($scope, $http) {
$scope.childName = 'Child!!'
});

You cannot use 2 ng-app attribute on a page.
However, looking at your requirement, I think you need to use 2 controllers and do some stuff with it while maintaining the appearance of parent-child in the HTML structure. To, do that you can make use of the angular.bootstrap method.
So, you can modify the html as below:
<div id="parentApp" ng-cloak="" ng-controller="mainController">
<div id="someContent">
{{$scope.parentName}}
***some parent app actions***
</div>
<div id="childApp" ng-app="childApp">
<div id="someContent" ng-controller="secondController">
{{$scope.childName}}
***some child app actions***
</div>
</div>
</div>
And in your code, you can initialize it as below:
var parentAppDivId = document.getElementById('parentApp');
angular.bootstrap(parentAppDivId, ['parentApp']);
var parentApp = angular.module('parentApp', []);
parentApp.controller('mainController', function($scope, $http) {
$scope.parentName = 'Parent!!'
});
var childAppDivId = document.getElementById('childApp');
angular.bootstrap(childAppDivId, ['childApp']);
var childApp = angular.module('childApp', []);
childApp.controller('secondController', function($scope, $http) {
$scope.childName = 'Child!!'
});

If you already have two separate apps and are trying to leverage parts of one in another app, you can inject the module from one app into another. It's the the same structure as you've outlined above, but it will make everything from the first app available in the second app.
angular.module('childApp', ['parentApp'])...

Angular.js output value live on ng-click

I'm new to angular and little bit confused with it. So basically I created a simple button and i want to run function foo() whitch assigns variable var one = 1; to $scope and outputs it in <p>{{one}}<p> every time its clicked like in live typing but this seems not working. Please provide me a solution to this.
<html ng-app="app">
<!-- Body tag augmented with ngController directive -->
<body ng-controller="myController">
<input type="text" ng-model="name">
<p>{{name}}</p>
<p>{{one}}</p>
<button ng-click="foo()">1</button>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.5.6/angular.min.js"></script>
<script src="controller.js"></script>
</body>
</html>
controller:
var app = angular.module('app',[]);
app.controller('myController', ['$scope',function($scope){
var one = 1;
$scope.name = name;
function foo(){
return $scope.one = one;
}
}]);

function foo() dont exist in $scope your controller "myController"
if you declaration:
$scope.foo = function(){}
in your controller, then this work for you

when you are calling controller function from the html, controller function should be scope. Other wise ng-click directive doesn't recognize the function.
same concept goes to binding variable to html. only scope variables can directly bind to html using curly brackets. so inside foo function var one should assign to scope.one in order to display it in the html.
angular.module("app",[])
.controller("ctrl",function($scope){
var one = 1;
$scope.name = name;
$scope.foo = function(){
$scope.one = one;
}
})
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.22/angular.min.js"></script>
<div ng-app="app" ng-controller="ctrl">
<input type="text" ng-model="name">
<p>{{name}}</p>
<p>{{one}}</p>
<button ng-click="foo()">1</button>
</div>

How to let the angularjs controller run only once even many ng-controllers defined in DOM?

I wish I can handle this, but in the bad way...namely I need to use $cookieStore to check either the function called or not.
Every time to use push array then I need to use $cookieStore. But it seems not practical.
Here was my DOM:
<div ng-controller="MyCtrl">
<div>
<div ng-include="'temp2.html'">
Hello, {{name}}!
</div>
</div>
</div>
<script type="text/ng-template" id="temp2.html">
<div ng-controller="MyCtrl">Another View</div>
</script>
And my angularjs controller:
var myApp = angular.module('myApp',[]);
//myApp.directive('myDirective', function() {});
//myApp.factory('myService', function() {});
function MyCtrl($scope) {
$scope.name = 'Superhero';
alert(1);
}
alert(1) function will be called 2 times every times the page was called.
How to avoid this problem without using watcher?
My fiddle for your convenience. Thanks!

The controller would called be twice for both the views, i would suggest you to move controller specific code to init function and use ng-init in one of your views.
var Controller = function($scope) {
$scope.init = function () {
};
};
Your View
<div ng-controller="Controller" ng-init="init()"/>

Yo don't need to specify the Controller name again in the include.... if its the same as the parent one(same as controller of main page).
just go with this
<div ng-controller="MyCtrl">
<div>
<div ng-include="'temp2.html'">
Hello, {{name}}!
</div>
</div>
</div>
<script type="text/ng-template" id="temp2.html">
<div>Another View {{name}}</div>
</script>
Js Fiddel
name will be accessible in the view you included.
Hope it will help you..

Does angular.equals() work as an angular expressions?

I'm trying to display a div if an object is non-empty. Using this answer, Im trying to use angular.equals to check emptyness, but its not behaving as expected
var test = angular.module('test',[]);
test.controller('testCtrl', ['$scope', function($scope){
$scope.foo={};
$scope.bar="bam"
}]);
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app="test">
<div ng-controller="testCtrl">
<div ng-show="!angular.equals(foo,{})">{{bar}}</div>
</div>
</div>
The expectation here is that the value of bar will only show if foo is not equal to an empty object. However, foo is clearly set to {} and yet bar still shows.

If you want to access the angular object from templates or expressions, you have to make it available on the scope of where you want to use it. In this case you can put it on the testCtrl's scope.
var test = angular.module('test',[]);
test.controller('testCtrl', ['$scope', function($scope){
$scope.angular = angular;
$scope.foo={};
$scope.bar="bam"
}]);
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app="test">
<div ng-controller="testCtrl">
<div ng-show="!angular.equals(foo,{})">{{bar}}</div>
</div>
</div>
I generally put utility objects on $rootScope, so they're available from everywhere.

A cleaner way would be to only add the angular equals method to the $scope:
var test = angular.module('test',[]);
test.controller('testCtrl', ['$scope', function($scope){
$scope.angularEquals = angular.equals;
}
Then you can use the equals method in the template, like:
<div ng-show="!angularEquals(foo,{})">{{bar}}</div>

Your view is looking for a function on the scope, and $scope.angular.equals does not exist. You need to write one like this:
var test = angular.module('test', []);
test.controller('testCtrl', ['$scope',
function($scope) {
$scope.foo = {};
$scope.bar = "bam";
$scope.isEmpty = function(obj) {
return angular.equals(obj,{});
};
}
]);
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app="test">
<div ng-controller="testCtrl">
<div ng-hide="isEmpty(foo)">{{bar}}</div>
</div>
</div>

Angular functions can't be used inline, AFAIK.
You could do the equal check with a function inside the controller instead and return the result.