angularjs - Why does ng-click not work in case-1, but does in case-3? -

there fundamental im not yet understanding.

im trying make user of modal module in angular ui.bootstrap im finding clicks not activating open() function -- boiling down simple testcase, below, im not seeing calls when ng-click points function (alert or console.log), work when ng-click points expression

why alert not called in first example?

<div data-ng-app>     <button data-ng-click="alert('message 1');">         ngclick -- not working, why not?     </button>     <button onclick="alert('message 2');">         plain onclick     </button>     <button data-ng-click="count = (count + 1)">           works, why ???     </button>     count: {{count}} </div> 

http://jsfiddle.net/h2wft/1/

ng-click meant use either function in current scope (so example $scope.alert = window.alert solve problem of not being able alert there) or angular expression. looks angular not allow use global scope methods in there (it might looking them in current $scope, missing).