Trigger a button (without id) or his related function from UIWebview (iOS)

How can I trigger this button:

<button ng-click="lc.login()" ng-show="!lc.isLoggingIn" class="mdl-button mdl-js-button mdl-button--raised mdl-button--colored mdl-js-ripple-effect ng-binding" data-upgraded=",MaterialButton,MaterialRipple">Sign in<span class="mdl-button__ripple-container"><span class="mdl-ripple is-animating" style="width: 155.883px; height: 155.883px; transform: translate(-50%, -50%) translate(41px, 14px);"></span></span></button>

from an UIWebwiew.

I already tried many things none are working :

[self.webview stringByEvaluatingJavaScriptFromString: @"lc.login()"];

[self.webview stringByEvaluatingJavaScriptFromString: @"document.querySelectorAll(angular.element(domElement).triggerHandler('lc.login')"];