Ternary operator in AngularJS templates

How do you do a ternary with AngularJS (in the templates)?

It would be nice to use some in html attributes (classes and style) instead of creating and calling a function of the controller.

Answer

Update: Angular 1.1.5 added a ternary operator, so now we can simply write

<li ng-class="$first ? 'firstRow' : 'nonFirstRow'">

If you are using an earlier version of Angular, your two choices are:

  1. (condition && result_if_true || !condition && result_if_false)
  2. {true: 'result_if_true', false: 'result_if_false'}[condition]

item 2. above creates an object with two properties. The array syntax is used to select either the property with name true or the property with name false, and return the associated value.

E.g.,

<li class="{{{true: 'myClass1 myClass2', false: ''}[$first]}}">...</li>
 or
<li ng-class="{true: 'myClass1 myClass2', false: ''}[$first]">...</li>

$first is set to true inside an ng-repeat for the first element, so the above would apply class ‘myClass1’ and ‘myClass2’ only the first time through the loop.

With ng-class there is an easier way though: ng-class takes an expression that must evaluate to one of the following:

  1. a string of space-delimited class names
  2. an array of class names
  3. a map/object of class names to boolean values.

An example of 1) was given above. Here is an example of 3, which I think reads much better:

 <li ng-class="{myClass: $first, anotherClass: $index == 2}">...</li>

The first time through an ng-repeat loop, class myClass is added. The 3rd time through ($index starts at 0), class anotherClass is added.

ng-style takes an expression that must evaluate to a map/object of CSS style names to CSS values. E.g.,

 <li ng-style="{true: {color: 'red'}, false: {}}[$first]">...</li>

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