Edit in JSFiddle


              
<div ng-init="test=0">
Test: {{test}}
<br>
<button disabled ng-click="test=test+1">
disabled
</button>
<br>
<button disabled="disabled" ng-click="test=test+1">
disabled="disabled"
</button>
<br>
<button disabled="true" ng-click="test=test+1">
disabled="true"
</button>
    
<br>
<button disabled="false" ng-click="test=test+1">
disabled="false"
</button>
    
<br>
<button disabled="" ng-click="test=test+1">
disabled=""
</button>
    
    <br>
<button ng-disabled ng-click="test=test+1">
ng-disabled
</button>
<br>
<button ng-disabled="disabled" ng-click="test=test+1">
ng-disabled="disabled"
</button>
<br>
<button ng-disabled=" 'disabled' " ng-click="test=test+1">
ng-disabled=" 'disabled' "
</button>
<br>
<button ng-disabled="true" ng-click="test=test+1">
ng-disabled="true"
</button>
    
<br>
<button ng-disabled="false" ng-click="test=test+1">
ng-disabled="false"
</button>
    
<br>
<button ng-disabled="" ng-click="test=test+1">
ng-disabled=""
</button>
    
</div>