Example: Utilizing data transfer from model to directive

Question

Example: Utilizing data transfer from model to directive

I have a question regarding a specific part in an example from Thinkster. I believe my confusion is due to my limited understanding of JavaScript and AngularJS fundamentals. I've been teaching myself since December, starting with the basics of JavaScript and now diving into Angular. If you could explain it to me as if I were 5 years old, I would greatly appreciate it! Check out the Thinkster Page here

App.js

app.controller("ChoreCtrl", function($scope){
  $scope.logChore = function(chore){
    alert(chore + " is done!");
  };
});

app.directive("kid", function() {
   return {
    restrict: "E",
    scope: {
    done: "&"
   },
    template: '<input type="text" ng-model="chore">' +
    //I'm slightly confused about this particular section

      '{{chore}}' +
      '<div class="button" ng-click="done({chore: chore})">I\'m done</div>'
  };
});

HTML

<div ng-app="choreApp">
     <div ng-controller="ChoreCtrl">
        <kid done="logChore(chore)"></kid>
     </div>
</div>

How does {chore:chore} actually work? According to Thinkster:

The {chore:chore} syntax links the chore value from the input model to be passed to the logChore function when we use 'done="logChore(chore)"' (in the kid directive)

Here are my thoughts:

Clicking invokes "done", which further triggers "logChore(chore)" based on the HTML attribute
I assume that "{chore:chore}" in App.js is being passed to logChore, so it's like calling logChore(chore:chore)?

Why can't we simply use ng-click=(done(chore))? What is exactly happening with {chore:chore}? It might be obvious that I am pretty lost in all this haha.

Thank you very much for your help!

javascript angularjs

Answer 1

Answer №1

The reason for this behavior is due to the use of the & operator, which you can understand more deeply by referring to this link: https://docs.angularjs.org/api/ng/service/$compile#-scope-

Here's what it means:

The & or &attr - provides a way to execute an expression in the context of the parent scope. If no attr name is specified then the attribute name is assumed to be the same as the local name.

In simple terms, this allows us to access the `chore` property of the parent scope, as without it we would be limited to the directive's isolate scope where `chore` property does not exist.

You can also check out further explanation at:

To enhance clarity, I've made some modifications to the code. Now, we have property names like `innerChore`, `outerChore`, and `param` to prevent any naming conflicts:

var app = angular.module('choreApp', []);

app.controller("ChoreCtrl", function($scope){
  $scope.logChore = function(param){
    alert(param + " is done!");
  };
});

app.directive("kid", function() {
  return {
    restrict: "E",
    scope: {
        done: "&"
      },
    template: '<input type="text" ng-model="innerChore">' +
      '{{innerChore}}' +
      '<div class="button" ng-click="done({outerChore: innerChore})">I\'m done</div>'
  };
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.4.7/angular.min.js"></script>
<div ng-app="choreApp">
  <div ng-controller="ChoreCtrl">
    <kid done="logChore(outerChore)"></kid>
  </div>
</div>

Pay attention to the relationship shown in {outerChore: innerChore}.

Answer 2

The reason for this behavior is due to the use of the & operator, which you can understand more deeply by referring to this link: https://docs.angularjs.org/api/ng/service/$compile#-scope-

Here's what it means:

The & or &attr - provides a way to execute an expression in the context of the parent scope. If no attr name is specified then the attribute name is assumed to be the same as the local name.

In simple terms, this allows us to access the `chore` property of the parent scope, as without it we would be limited to the directive's isolate scope where `chore` property does not exist.

You can also check out further explanation at:

To enhance clarity, I've made some modifications to the code. Now, we have property names like `innerChore`, `outerChore`, and `param` to prevent any naming conflicts:

var app = angular.module('choreApp', []);

app.controller("ChoreCtrl", function($scope){
  $scope.logChore = function(param){
    alert(param + " is done!");
  };
});

app.directive("kid", function() {
  return {
    restrict: "E",
    scope: {
        done: "&"
      },
    template: '<input type="text" ng-model="innerChore">' +
      '{{innerChore}}' +
      '<div class="button" ng-click="done({outerChore: innerChore})">I\'m done</div>'
  };
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.4.7/angular.min.js"></script>
<div ng-app="choreApp">
  <div ng-controller="ChoreCtrl">
    <kid done="logChore(outerChore)"></kid>
  </div>
</div>

Pay attention to the relationship shown in {outerChore: innerChore}.

Answer 3

Answer №2

Consider the meaning behind the done attribute expression: logErrand(errand). This code is evaluated within the context of the $scope for the ErrandCtrl (meaning that all variables and functions must be part of that specific scope). So, let's examine which variables and functions are being referenced here: logErrand() and errand. It's clear that logErrand() is a defined function property on the $scope, but what about errand? It doesn't exist on the $scope object at all!

Now, when you invoke .done() within the directive's link() function, you provide a locals map that specifies values for variables, overriding any existing ones on the $scope. In this scenario, using {errand: errand} means "utilize the errand object from the directive's isolated scope as the value for the errand variable in the specified expression for the done attribute." Suddenly, we have clarity on what errand represents in the logErrand(errand) expression.

Does this explanation offer more insight?

Answer 4

Consider the meaning behind the done attribute expression: logErrand(errand). This code is evaluated within the context of the $scope for the ErrandCtrl (meaning that all variables and functions must be part of that specific scope). So, let's examine which variables and functions are being referenced here: logErrand() and errand. It's clear that logErrand() is a defined function property on the $scope, but what about errand? It doesn't exist on the $scope object at all!

Now, when you invoke .done() within the directive's link() function, you provide a locals map that specifies values for variables, overriding any existing ones on the $scope. In this scenario, using {errand: errand} means "utilize the errand object from the directive's isolated scope as the value for the errand variable in the specified expression for the done attribute." Suddenly, we have clarity on what errand represents in the logErrand(errand) expression.

Does this explanation offer more insight?

Example: Utilizing data transfer from model to directive

Answer №1

Answer №2

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