Cutom Backpack

[hexed osprey]

Creating a custom backpack is quite challenging, but there are some ways to make it work.
First, you’ll need a powerful JS 1.7.0 build. Since it's not yet published, you’ll need to build it yourself. (I may release a continuation once I figure out how to bind containers with item handlers and the interation of create stress system.)
For now, all we can do is hoping Prunoideae publishes the item handler.

StartUp scripts:

StartupEvents.registry("item", event => {
    event.create("backpack", "basic")
    .maxStackSize(1)
    .attachCapability(CapabilityBuilder.ITEM.itemStack(27))
});

ServerScripts:

[tight iris]

Paste version of backpack.js from @hexed osprey

[hexed osprey]

You can use NBT to store items instead of relying on powerfuljs, making a basic backpack is possible with KubeJS.
Althought it sucks

const $CompoundTag = Java.loadClass("net.minecraft.nbt.CompoundTag");

[proven tulip]

Would it be hard to add restriction of what kind of items you can store in the container?

[crisp swallow]

oooooh can I get some more info on this? I need to make items that store numbers and enums

[hexed osprey]

Basically you need to download the source codes if PowerfulJS and build it first.

[hexed osprey]

It's a kind of "Fake Chest". So sadlly you can't : ( I'm finding a way of archiving it.
And I thought Menu JS which hasn't been released will support it.

[echo finch]

can you add this to a curios slot and then have the open inv set to a keybind? or make it like a portable ender chest :0

[hexed osprey]

Sounds intersting. Actually available, cuiros is almost data driven.

[echo finch]

do you think its doable?

[hexed osprey]

Doable and not that hard.