Angular library uses document.documentMode to identify IE . It holds major version number for IE, or NaN/undefined if User Agent is not IE.
/**
* documentMode is an IE-only property
* http://msdn.microsoft.com/en-us/library/ie/cc196988(v=vs.85).aspx
*/
var msie = document.documentMode;
https://github.com/angular/angular.js/blob/v1.5.0/src/Angular.js#L167-L171
Example with $document (angular wrapper for window.document)
// var msie = document.documentMode;
var msie = $document[0].documentMode;
// if is IE (documentMode contains IE version)
if (msie) {
// IE logic here
if (msie === 9) {
// IE 9 logic here
}
}