Lazy rendering paper-submenu

[NamTThai]

Description

I have a paper-menu with many paper-submenus, depth=3. Imagine a directory with 2 layers of subdirectories. Each menu only has 10-15 submenus, each depth 3 submenu only has 25-50 items. However, the total grows fast. On an instance which I have 16,000 items, the paper-menu takes 10 seconds to render on screen. It is generated by dom-repeat.

Expected outcome

Lazy render :D/? Something similar to what iron-list do, which only render items visible in viewport. The client only need to see items in depth 1 submenu at first. The rest can be rendered gradually.

Actual outcome

The entire menu takes 10 seconds to render on screen