nextcloud-server/core/js/publicshareauth.js

document.addEventListener('DOMContentLoaded', function() {
	var passwordInput = document.getElementById('password');
	var passwordButton = document.getElementById('password-submit');
	var eventListener = function() {
		passwordButton.disabled = passwordInput.value.length === 0;
	};

	passwordInput.addEventListener('click', eventListener);
	passwordInput.addEventListener('keyup', eventListener);
	passwordInput.addEventListener('change', eventListener);
});