I currently have an onclick event that switches classes like this:
....
<button id="@m.TargetCo.ButtonId" onclick="glyphChanger(this.id)" class="btn btn-default iconButton glyphicon glyphicon-chevron-right" ></button>
....
function glyphChanger(buttonID) {
$("#" + buttonID).toggleClass('glyphicon-chevron-right glyphicon-chevron-up');
} 
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No JavaScript required. You can do this the Blazor way.
DropDownComponent.razor
Elsewhere in the app