How to write angular directive that toggles classes by selector

Question

I'm trying to write a directive that toggles classes based on a selector condition:

<label class-when="{'is-checked': ':has(input:checked)', 'is-disabled': ':has(input:disabled)'}">
    <input type="checkbox">
    Example checkbox
</label>

I need to somehow watch for DOM changes on the element and its descendents but I'm getting an ng:areq error. How can I do this?

define(function (require) {
    var _ = require('lodash');

    return {
        restrict: 'A',
        scope: {
            object: '@classWhen'
        },
        link: function (scope, element) {
            scope.$watchCollection(function() {
                return element.find('*').add(element);
            }, function () {
                _.forOwn(scope.object, function (test, classes) {
                    test = typeof test === 'boolean' ? test : element.is(test);
                    element.toggleClass(classes, test);
                });
            });
        }
    };
});

Answer 1

I have created a generic fiddle for this and also with RequireJS as you used.

Please have a look here

http://fiddle.jshell.net/balasuar/dugmu/15/

Note: Whatever property you added in the selector like :checked and :disabled, add the related angular property to the child element like ng-model and ng-disabled. It will work like a charm !!

Code

var app = window.app = angular.module("myApp", []);

define('classWhenDirective', function () {
    //var _ = require('lodash');
    var app = window.app;debugger;
    app.directive("classWhen", function() {
    return {
    restrict: 'A',
    link: function(scope, element, attrs) {
          scope.$watch(getChanges, setClasses)

  function getChanges() {
    var attrs = [];
    
    function getAttrs(elm) {
       $.each(elm.attributes, function(i, attrib){
     var name = attrib.name;
     var value = attrib.value;
       if(value && name.indexOf('ng-') > -1) {
         value = scope.$eval(value);
       }
     if(value) {      
       attrs.push(name + ':' + value);
     }
  });
     
    }
    
    getAttrs(element.get(0));
    
    element.children().each(function(){
       getAttrs(this);
    });
    
    return attrs.join(',');
  }

  function setClasses() {
    var rawClasses = scope.$eval(attrs.classWhen);

    Object.keys(rawClasses).forEach(function(className){
      var expr = rawClasses[className]
      var setClass = typeof expr === 'string'
        ? element.is(expr)
        : !!expr;
       element.toggleClass(className, setClass);
    });
  }
    }
  };   
    });
});

define('todo', ['classWhenDirective'], function() {
  var app = window.app;
  app.controller('myController', function($scope) {

  });
});

// angular bootstrap
require(['todo'], function() {
  angular.bootstrap(document, ['myApp']);
});

.is-checked {
  color: green;
}
.is-disabled {
  color: gray;
}

<script src="http://requirejs.org/docs/release/2.0.6/minified/require.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<h2>ClassWhen Directive</h2>

<div ng-controller="myController">
  <label>
    <input type="checkbox" ng-model="disableAll" />Disable All</label>
  <br>
  <br>
  <label class-when='{"is-checked": ":has(input:checked)", "is-disabled": ":has(input:disabled)"}'>
    <input type="checkbox" ng-model="checkBox1" ng-disabled="disableAll">ClassWhen checkbox 1
  </label>
  <br>
  <label class-when='{"is-checked": ":has(input:checked)", "is-disabled": ":has(input:disabled)"}'>
    <input type="checkbox" ng-model="checkBox2" ng-disabled="disableAll">ClassWhen checkbox 2
  </label>
</div>

Answer 2

Here's my attempt to solve your problem in generic way: https://plnkr.co/edit/kVyJQClmQhF3FeBTmKaX?p=preview

Directive code:

app.directive('classWhen', () => (scope, element, attrs) => {
  scope.$watchCollection(getClasses, setClasses)

  function getClasses() {
    // We have to evaluate expression in attrs.classWhen so that we get object
    const rawClasses = scope.$eval(attrs.classWhen)
    const classes = {}

    // then we normalize it so that strings are treated as jquery selectors
    Object.keys(rawClasses).forEach((className) => {
      const expr = rawClasses[className]
      classes[className] = typeof expr === 'string'
        ? element.is(expr)
        : !!expr // we normalize falsy values to booleans
    })

    // then we return it to $watchCollection
    return classes
  }

  /**
   * will be called whenever any of the classes changes
   */
  function setClasses(classes) {
    Object.keys(classes).forEach((className) => {
      element.toggleClass(className, classes[className])
    })
  }
})

Answer 3

Okay, after reading your bounty comment, I understand that you want this to be controller independent. I spent some time completely reworking my solution, and I think I have finally figured out a way to accomplish what you want.

It really comes down to 2 things:

1) Detecting a change on the checkbox :checked status, and

2) Detecting a change on the checkbox :disabled status

Detecting 1) was easy, as you can use a simple jQuery change handler, but detecting 2) took a bit more research. It requires the use of scope.$watch on the child ng-disabled attribute.

Here is a demo of how this would work:

var app = angular.module("myApp", [])
  .directive("classWhen", function() {
    function setClasses(classWhen, $element, $input) {
      Object.keys(classWhen).forEach(function(key) {
        var test = classWhen[key];
        // .toggleClass("className", true) === .addClass("className")
        // .toggleClass("className", false) === .removeClass("className")
        $element.toggleClass(key, $element.is(test));
      });
    }
    return {
      restrict: 'A',
      link: function link (scope, element, attrs) {
        var classWhen = JSON.parse(attrs.classWhen);
        var $element = $(element);
        $element.find("*").each(function (index, elem) {
          var $elem = $(this);
          // namespace the change event so we can easily .off() it
          $elem.off("change.classWhen");
          $elem.on("change.classWhen", function () {
            setClasses(classWhen, $element, $elem);
          });
          // watch child ng-disabled attribute
          scope.$watch($elem.attr("ng-disabled"), function (val) {
            setClasses(classWhen, $element, $elem);
          });
        });
      }
    };
  });

.is-checked {
  background-color: yellow;
}
.is-disabled {
  background-color: lightblue;
}

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div ng-app="myApp">
  <label>
    <input type="checkbox" ng-model="disableAll" />Disable All</label>
  <br>
  <br>
  <label class-when='{"is-checked": ":has(input:checked)", "is-disabled": ":has(input:disabled)"}'>
    <input type="checkbox" ng-disabled="disableAll">Example checkbox 1
  </label>
  <br>
  <label class-when='{"is-checked": ":has(input:checked)", "is-disabled": ":has(input:disabled)"}'>
    <input type="checkbox" ng-disabled="disableAll">Example checkbox 2
  </label>
  <br>
  <label class-when='{"is-checked": ":has(input:checked, .test)", "is-disabled": ":has(input:disabled)"}'>
    <input type="text" ng-disabled="disableAll" ng-class="testingClass" ng-model="testingClass"/>
    <br>
    <input type="checkbox" ng-disabled="disableAll">
    Example checkbox 3
  </label>
  <br>
  <label class-when='{"is-checked": ":has(input:checked)", "is-disabled": ":has(input:disabled)"}'>
    <input type="checkbox" ng-disabled="disableAll">Example checkbox 4
  </label>
</div>