4

I want to create a $scope function that will only manipulate the variables that it receives.

I've made a working Plunker to test things out.

I have a ng-repeat that is just listing names and id of kitties. I also have an input form to receive a name of a new kitty. Then, I have 3 buttons, each one accessing a different $scope function that will manipulate the $scope in different ways.

The goal of every function is to read the name of the kitty from the input form, read the last id used on the kitties array, assign that id+1 to the new kitty, push the new kitty to the array of kitties and delete the form data.

  • The first function, $scope.addFullScope(), will receive nothing as arguments and will read and manipulate everything from $scope.

  • The second function, $scope.addJustDelete(kitty, kitties), will receive both the new kitty and the kitties array as argument. But, on the end, to clean up the form, it will do $scope.kitty = undefined

  • The third function, $scope.addNoScope(kitty, kitties), will receive both the new kitty and the kitties array as argument. But, on the end, to clean up the form, it will do kitty = undefined. But the form won't clean up! and everything will star to bug out.

How can I make this third function, or something like it, work so I have a fully independent function to work with?

Appendix:

Html:

  <body ng-app='app' ng-controller="ctrl">

    <h3 ng-repeat="kitty in kitties">
      {{kitty.name}}: {{kitty.id}} //Kitties list
    </h3>

    <input placeholder='Kitty name to add' class='form form-control' 
           type="text" ng-model="kitty.name" />

    <h3> $scope use on adding kitty:</h3>
    <button ng-click="addFullScope()">Full Scope.</button>
    <button ng-click="addJustDelete(kitty, kitties)">Just delete.</button>
    <button ng-click="addNoScope(kitty, kitties)">None. Buggy</button>
  </body>

Controller:

.controller('ctrl', function($scope) {
  $scope.kitties = [
    //Let's imagine kitties in here.
    {name: 'Purple kitty', id:35},
    //Kittie 36 died in a car accident. :(
    {name: 'Rodmentou cat', id: 37},
    {name: 'Fatty kitty', id: 38}

    ];

  $scope.addFullScope = function () {
    var size = $scope.kitties.length;
    var id = $scope.kitties[size-1].id + 1;

    $scope.kitty.id = id;
    $scope.kitties.push($scope.kitty);
    $scope.kitty = undefined;
  };

  $scope.addJustDelete = function (kitty, kitties) {
    var size = kitties.length;
    var id = kitties[size-1].id + 1;

    kitty.id = id;
    kitties.push(kitty);
    $scope.kitty= undefined;

  };

  $scope.addNoScope = function (kitty, kitties) {
    var size = kitties.length;
    var id = kitties[size-1].id + 1;

    kitty.id = id;
    kitties.push(kitty);
    kitty = undefined; //Don't work
  };



});
Rodmentou
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    This is the same as why `var a=99;(function(a){a=0;})(a);console.log(a);` prints `99`. Objects are passed by reference, `addNoScope` just makes the local variable to reference `undefined` instead of the original object, but it is not deleted. – Tamas Hegedus Dec 03 '15 at 15:50
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    You can't have a form that is using `$scope` for its model, and expect a function to manipulate that form without touching `$scope` – Oli Dec 03 '15 at 15:52
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    You should be using a service instead of manipulating the $scope. A kittenService could expose a kittens list and a method to push a new one where it would handle the id generation. – Aaron Dec 03 '15 at 15:58
  • The only thing I'm especting is an answer on how to delete The form without touching scope. – Rodmentou Dec 03 '15 at 16:00

5 Answers5

9

Under the hood Angular needs a way to watch if a ngModel is changed and uses $scope.$watch to accomplish this. $watch is considered a Equality Watcher, where it checks if one specific property has changed and not if the object underlying it has changed, which would be a Reference Watcher.

I found a good description and image of this on Tero Parviainen's blog

enter image description here

So the issue with your code is that you are setting kitty = undefined, but ngModel and by extension $scope.$watch is looking for a change in kitty.name. To prove this was the case I added a watch on kitty.name and when you set kitty = undefined the watch never gets triggered. Setting kitty to undefined changes the underlying object, but not it's properties (pretty confusing)! I created a plunker example with updated code.

HTML

For clarity sake, I made the model we are updating kitten so it is not confused with the kitties we are iterating over. 

<h3 ng-repeat="kitty in kitties">
  {{kitty.name}}: {{kitty.id}}
</h3>
<input placeholder='Kitty name to add' class='form form-control' type="text" ng-model="kitten.name" />
<h3> $scope use on adding kitty:</h3>
<button class='btn btn-success' ng-click="addNoScope(kitten, kitties)">None. Buggy</button>
<button class='btn btn-danger' ng-click="noWatch(kitten)">Full Scope.</button>

Javascript

The big update is creating a clone kitten out of the model's kitten, so that it is not referenced within the array. Also when we want to reset the model's kitten we set the kitten.name and kitten.id properties directly. 

angular.module('app', [])
.controller('ctrl', function($scope) {

  $scope.kitten = {
    name: undefined, id: undefined
  };

  $scope.$watch('kitten.name', function() { console.log("changed"); }, true);

  $scope.kitties = [
    //Let's imagine kitties in here.
    {name: 'Purple kitty', id:35},
    //Kittie 36 died in a car accident. :(
    {name: 'Rodmentou cat', id: 37},
    {name: 'Fatty kitty', id: 38}

  ];

  $scope.addNoScope = function (kitten, kitties) {
    if (!$scope.kitten || !$scope.kitten.name) return;
    var size = kitties.length;
    var id = kitties[size-1].id + 1;
    var newKitten = {
      name: kitten.name, id: id
    }
    kitties.push(newKitten);
    kitten.name = undefined;
    kitten.id = undefined;
    // kitten = undefined;
  };

  $scope.noWatch = function (kitten) {
    kitten = undefined;
    console.log('not watching');
  };

});
jjbskir
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  • and if you don't prefer to manually clone the object you can use: var newKitten = JSON.parse(JSON.stringify(kitten)) – gafi Dec 14 '15 at 04:18
3

That's because the function $scope.addNoScope(kitty, kitties) receives only a "copy of the reference" to the object kitty, so changing the reference only affects this copy and not the original reference. Check this thread.

So in your case $scope.kitty remains pointing to the same object with the last name and id. And when you press addNoScope another time angular tries to push the same object again, which throws this error as angular does not allow duplicates in an ng-repeat unless you add track by.

The solution, if you need to do this without using the scope, is to pass an object that contains kitty as a property, so that when you change a property of the passed object, it reflects on the original object, as in this example

var obj = {id:1};

function changeReference (obj){ 
    //changing the reference to an entirely new object
    obj = {id:2}
}

function changeProperty (obj){ 
    //changing a property of the current object
    obj.id = 2
}

changeReference(obj);
console.log(obj.id);
//1 as original obj is not affected

changeProperty(obj);
console.log(obj.id);
//2

So your code becomes

$scope.addNoScope = function (fields, kitties) {
    var size = kitties.length;
    var id = kitties[size-1].id + 1;

    fields.kitty.id = id;
    kitties.push(fields.kitty);
    fields.kitty = undefined; //Don't work
  };

and the html

<input placeholder='Kitty name to add' class='form form-control' type="text" ng-model="fields.kitty.name" />
<h3> $scope use on adding kitty:</h3>
<button class='btn btn-danger' ng-click="addFullScope()">Full Scope.</button>
<button class='btn btn-warning' ng-click="addJustDelete(fields.kitty, kitties)">Just delete.</button>
<button class='btn btn-success' ng-click="addNoScope(fields, kitties)">None. Buggy</button>

and don't forget to change $scope.kitty to $scope.fields.kitty in the other functions or they will break.

Community
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gafi
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2

To use a independent function for the manipulating of kitties, and use a seperate function for the resetting of the form, try this:

  $scope.addNoScope = function (kitty, kitties) {
    manipulateKitties(kitty, kitties);
    resetForm();
  };

  function manipulateKitties(kitty, kitties) {
    var size = kitties.length;
    var id = kitties[size-1].id + 1;

    kitty.id = id;
    kitties.push(kitty);
  }

  function resetForm() {
    $scope.kitty= undefined;
  }
Oli
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1

This cannot be done as JS follows Java's method of pass-by-ref-ish argument passing. Here's some examples that are fairly relevant to your case

(pen)

    function double(x) {
      x.val = 2 * x.val;
    }

    function doubleToo(x) {
      x = 2 * x;
    }

    var data = {
      val: 2
    };

    document.write("Initial: " + data.val + "<br />");

    double(data); //data.val now = 4

    document.write("Double: " + data.val + "<br />");

    doubleToo(data.val); //data.val is still 4

    document.write("DoubleToo:" + data.val);

Assignment operations on arguments have no effect on the actual variable passed in. That's why the first example, which updates an object's contents has an effect, and the second (which tries to re-assign the value all-together) does not.

So in your case, if that function absolutely positively had to update a variable in $scope, it would have to receive $scope as a parameter (or some object containing a reference to $scope). Just like how in that example, it had to receive data to update data.val at all.

CollinD
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0

You just need to refactor your function on the following way:

  $scope.addNoScope = function (kitty, kitties) {
    var size = kitties.length;

    kitties.push({ //you need to create a new object
      id : kitties[size-1].id + 1,
      name : kitty.name
    });
    kitty.name = undefined;   
};

What is important to keep in mind is that JavaScript pass variables by value so that means that the parameter kitty is actually the variable from the scope $scope.kitty. So you were pushing the actual scope variable into your array and then make it equal to undefined, that was the reason of the buggy results.

Fernando Catacora
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