Change button color after click in Angularjs

Answer 1

you can use ng-class Define a var like $scope.started = false; and inside you start function set it to true. On your button do this:

ng-class="{'btn-warning': started, 'btn-danger': !started}"

another way to write it:

ng-class="started && 'btn-warning' || !started && 'btn-danger'"

note: remove btn-danger from your curre class attribute

EDIT

The newer, more common way is the standard ternary operator (also easier to read):

ng-class="started ? 'btn-warning' : 'btn-danger'"