Shows preloader on page load and hides when JS starts. Why hides? Because there is no showPreloader variable in $scope.

angular_preloader.html

{% block preloader %}
    {% if user.is_authenticated %}
        <div data-ng-if="showPreloader">
            {% assign name="loadingText" %}{% trans "Loading..." %}{% endassign %}
            {% include 'inc/preloader.html' %}
        </div>
    {% endif %}
{% endblock %}