What is the best way to conditionally apply a class?

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Lets say you have an array that is rendered in a ul with an li for each element and a property on the controller called selectedIndex.

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难免孤独

2020-11-22 09:30

We can make a function to manage return class with condition

<script>
    angular.module('myapp', [])
            .controller('ExampleController', ['$scope', function ($scope) {
                $scope.MyColors = ['It is Red', 'It is Yellow', 'It is Blue', 'It is Green', 'It is Gray'];
                $scope.getClass = function (strValue) {
                    switch(strValue) {
                        case "It is Red":return "Red";break;
                        case "It is Yellow":return "Yellow";break;
                        case "It is Blue":return "Blue";break;
                        case "It is Green":return "Green";break;
                        case "It is Gray":return "Gray";break;
                    }
                }
        }]);
</script>

And then

<body ng-app="myapp" ng-controller="ExampleController">

<h2>AngularJS ng-class if example</h2>
<ul >
    <li ng-repeat="icolor in MyColors" >
        <p ng-class="[getClass(icolor), 'b']">{{icolor}}</p>
    </li>
</ul>
<hr/>
<p>Other way using : ng-class="{'class1' : expression1, 'class2' : expression2,'class3':expression2,...}"</p>
<ul>
    <li ng-repeat="icolor in MyColors">
        <p ng-class="{'Red':icolor=='It is Red','Yellow':icolor=='It is Yellow','Blue':icolor=='It is Blue','Green':icolor=='It is Green','Gray':icolor=='It is Gray'}" class="b">{{icolor}}</p>
    </li>
</ul>

You can refer to full code page at ng-class if example

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终归单人心

2020-11-22 09:31
If you don't want to put CSS class names into Controller like I do, here is an old trick that I use since pre-v1 days. We can write an expression that evaluates directly to a class name selected, no custom directives are necessary:
```
ng:class="{true:'selected', false:''}[$index==selectedIndex]"
```
Please note the old syntax with colon.

There is also a new better way of applying classes conditionally, like:
```
ng-class="{selected: $index==selectedIndex}"
```
Angular now supports expressions that return an object. Each property (name) of this object is now considered as a class name and is applied depending on its value.

However these ways are not functionally equal. Here is an example:
```
ng-class="{admin:'enabled', moderator:'disabled', '':'hidden'}[user.role]"
```
We could therefore reuse existing CSS classes by basically mapping a model property to a class name and at the same time keep CSS classes out of Controller code.
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谎友^

2020-11-22 09:31
ng-class supports an expression that must evaluate to either
1. A string of space-delimited class names, or
2. An array of class names, or
3. A map/object of class names to boolean values.
So, using form 3) we can simply write
```
ng-class="{'selected': $index==selectedIndex}"
```
See also How do I conditionally apply CSS styles in AngularJS? for a broader answer.

Update: Angular 1.1.5 has added support for a ternary operator, so if that construct is more familiar to you:
```
ng-class="($index==selectedIndex) ? 'selected' : ''"
```
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无人及你

2020-11-22 09:31

partial

  <div class="col-md-4 text-right">
      <a ng-class="campaign_range === 'thismonth' ? 'btn btn-blue' :  'btn btn-link'" href="#" ng-click='change_range("thismonth")'>This Month</a>
      <a ng-class="campaign_range === 'all' ? 'btn btn-blue' :  'btn btn-link'" href="#" ng-click='change_range("all")'>All Time</a>
  </div>

controller

  $scope.campaign_range = "all";
  $scope.change_range = function(range) { 
        if (range === "all")
        {
            $scope.campaign_range = "all"
        }
        else
        {  
            $scope.campaign_range = "thismonth"
        }
  };

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无人共我

2020-11-22 09:31
If you are using angular pre v1.1.5 (i.e. no ternary operator) and you still want an equivalent way to set a value in both conditions you can do something like this:
```
ng-class="{'class1':item.isReadOnly == false, 'class2':item.isReadOnly == true}"
```
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天命终不由人

2020-11-22 09:34
well i would suggest you to check condition in your controller with a function returning true or false .
```
<div class="week-wrap" ng-class="{today: getTodayForHighLight(todayDate, day.date)}">{{day.date}}</div>
```
and in your controller check the condition
```
$scope.getTodayForHighLight = function(today, date){
return (today == date);
}
```
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