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What is the best way to conditionally apply a class?

453

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. What would be the best way to add a class to the li with the index selectedIndex in AngularJS?

I am currently duplicating (by hand) the li code and adding the class to one of the li tags and using ng-show and ng-hide to show only one li per index.

  • CSS

  • asked 2 years ago
  • B Butts

2Answer


0

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 returns 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 kept CSS classes out of Controller code.

  • answered 2 years ago
  • Gul Hafiz

0

My favorite method is using the ternary expression.

ng-class="condition ? 'trueClass' : 'falseClass'"

Note: Incase you're using a older version of Angular you should use this instead,

ng-class="condition && 'trueClass' || 'falseClass'"
  • answered 2 years ago
  • Sunny Solu

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