In angular JS I use the "isNull" function, the problem is that the value I put in it is not null but not defined. How can you make it behave as if the undefined value were null?
Related
As I understand it Angular will automatically setup standard $watch's for any $scope defined value within a controller that correlates with a model in the view.
But let's say I want of these values to check for equality instead. So within the controller I'd add a $watch(..., ..., true).
Doesn't that mean that there are now two $watch's running for the same value, each with a different watch depth? And if so, should I remove the standard $watch that Angular setup initially in order to remove the redundant $watch and thereby increase performance?
No, I think we are just overriding default watch of the angular when we write watch for scope variable , even if we write equality true or false I think this will override default watch of angular
Trying to have 2 way binding on an AngularJS directive while using primitive objects is not working, for example:
<custom-directive ng-model="variable"></custom-directive>
how can this be achieved?
In order to have 2 way binding in javascript (not just angularjs), we have to pass an object (this is caused by javascript's evaluation strategy - can read more about it here https://en.wikipedia.org/wiki/Evaluation_strategy#Call_by_sharing). basically what is happening is that when we pass a primitive variable, its been passed by value and re-created, instead of been passed by reference. only objects are passed by reference.
So this issue can be solved by passing the variable's parent object, for example:
<custom-directive ng-model-name="variable" ng-model-parent="parentObj"></custom-directive>
and then, modifying in object in the directive as following:
parentObj[variable] = "whatever";
this way, we will keep the connection between the variable to the parentObj.
another option would be passing the model with the parent obj, for example:
<custom-directive ng-model="parentObj.variable"></custom-directive>
the dot is an important part of this example. its actually a best practice by angular to always pass variables with the parentObj-dot-property.
for additional information, angularjs actually has a documentation about it https://github.com/angular/angular.js/wiki/Understanding-Scopes
I just realized that if your directive isn't inside an ng-if it will work with primitive bindings. Maybe the problem is that your bind is inside an ng-if. Try to use ng-show instead. Maybe it will work.
Passing the primitive this way:
<custom-directive ng-model="parentObj.variable"></custom-directive>
This question already has answers here:
How to parseInt in Angular.js
(7 answers)
Closed 6 years ago.
I am scratching my head here. I am using angularJS and trying to use the expression that contains call to parseInt.
{{0 == 2}}
...prints out false as expected.)
However, when I am trying:
{{parseInt(0) == parseInt(2)}}
... it prints out... true !
How can this be possible?
Angular does not use JavaScript's eval() to evaluate expressions.
Instead Angular's $parse service processes these expressions.
Angular expressions do not have access to global variables like
window, document or location. This restriction is intentional. It
prevents accidental access to the global state – a common source of
subtle bugs.
Refer
In your html
Both parseInt(0) and parseInt(2) are undefined in your html.
So {{undefined==undefined}} is true.Beacause parseInt is a Javascript function.So you cant access the parseInt function in side {{}}. [Here parseInt is not a scope variable]
Solution
If you wish to do this,
define parseInt in your controller,
$scope.parseInt = parseInt;
Then you can use the parseInt method in your html
That's because parseInt is not defined in your scope.
http://jsfiddle.net/halirgb/Lvc0u55v/
You can't execute regular JS in an angular expression. Your expressions will be evaluated against the current scope. So, parseInt is undefined in the current scope.
If you set parseInt as a function reference, it will work.
$scope.parseInt = parseInt;
This is because the view is attached to the controller via scope.
So whatever we write in view either a variable or a function or anything it's rendered by appending $scope in front of it.
eg.
a is rendered as $scope.a in the view
So when we write parseInt, its rendered by $scope.parseInt which is not defined.
FIX- define $scope.parseInt = parseInt in the controller attached to the particular view
You have comparing both undefined values so result will be true.
You cannot call a javascript method(parseInt) via angular directives(ng-blur,ng-change,..) either you can achieve by making angular functions.
Solution 1:
{{0*1 == 2*1}}
Just do a trick to convert to Integer by multiply with 1 (0*1 = 0, 2*1 =1).
Solution 2:
{{parseInt(0) == parseInt(2)}}
Controller:
// To Convert specific format
$scope.parseInt = funtion(value){
return parseInt(value,10);
}
or
$scope.parseInt = parseInt;
reference here
I have a input field with model named "name" with some initialized value say "James".
And when i console $scope i can see model value as "James".
ie. $scope.name = "James".
But immediate on next statement if i use setTimeout function and update input field value with Say "Marcus" and console $scope again, why i get $scope.name = "James" only.
I know, i have updated input field value by going out of box than angular and angular is not aware of updation.
So my real question is, Is Angular JS written over Javascript Language? And if yes, why using setTimeout not updated model value in $scope.
Please help me, if i am thinking/question is right or wrong.
This has to do with how angular handles two way data-binding and the digest loop. If you're interested in knowing all the details of how this works then you can read about it here: https://www.ng-book.com/p/The-Digest-Loop-and-apply/
The basic idea is that in angular the digest loop is used to keep track of all the variables you placed in your $scope. Whenever a variable changes it sets off the digest loop, in each cycle of the loop the new value of the variable is compared to the old value and updated accordingly until the new value is equal to the old value which ends the loop. That being said this only works as long as you change your variables within angular's context, this is especially true for changing variables within callback functions or with jquery. Angular doesn't know that a variable was changed so the digest loop never gets started, you could force it by using $scope.$apply but some cases should be avoided in general unless there's no angular alternative for it (Which usually isnt the case).
For setTimeout there's an angular alternative which is $timeout, this has the exact same functionality as setTimeout but it works within angular's context so your variable will be updated.
I have a string reference to one of my scope values like this:
var reference_string = "form.name";
And I want to assign a value to the object it is referencing:
$scope.form.name = 'newvalue';
Looking around, I found 2 possible solutions: using plain JS or using the angular $parse function.
However, it seems like the $parse function only returns the value. Can I make it so that I can assign a new value?
ie. I want to do something like
var reference_string = "form.name";
var reference = getReference($scope, reference_string); // ideally using an angular in-built function like $parse
reference = 'newvalue'; // should have the same effect as $scope.form.name = 'newvalue';
The object returned by $parse has an assign() method for setting values.
var getter = $parse(reference_string);
getter.assign($scope, 'newValue');
Plunker demo ~ http://plnkr.co/edit/RlhXRpJvQ69ZdEkstyq8?p=preview
$parse is an Angular service which converts an expression into a function. The function can then be invoked and passed a context (usually scope) in order to retrieve the expression's value.
In addition, if the expression is assignable the returned function will have an assign property. The assign property is a function that can be used to change the expression's value on the given context.
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