In AngularJS when using ng-app: ng-app found in the document will be used to define the root element to auto-bootstrap as an application.
In some of the application it is being used as data-ng-app.
Is there any difference in both of the following declaration, If Yes what & If No then which one is significant and why ?
1.
<body ng-app>
<p>{{ 1 + 2 }}</p>
</body>
2.
<body data-ng-app>
<p>{{ 1 + 2 }}</p>
</body>
Both and are the same except for the fact that if you want your template/code to be according to be HTML compliant and follow the best practices. Use data-ng-app.
This is what the official documentation quotes:
"Best Practice: Prefer using the dash-delimited format (e.g. ng-bind for ngBind). If you want to use an HTML validating tool, you can instead use the data-prefixed version (e.g. data-ng-bind for ngBind). The other forms shown above are accepted for legacy reasons but we advise you to avoid them."
Hope that answers your question.
Cheers!
See the answer:
ng-app vs. data-ng-app, what is the difference?
Only diffrence regarding html5 validation
ng-app isn't strictly valid html. Custom attributes should be prefixed with data- to be valid.
So angular added this syntax so users could still have valid html. (Knockout also uses data- attributes.) There is absolutely no difference in functionality.
Source: w3.org - custom data attributes
ng-app and data-ng-app both are similar to each other, the only difference between them is sometimes HTML validators will show an error while using ng-app. so that time you can use data-ng-app.
note: x-ng-app also have the same property. You can use x-ng-app too instead of using data-ng-app.
来源：https://stackoverflow.com/questions/21110450/ng-app-v-s-data-ng-app-in-angularjs