validate-tree

Validates a rojo-esque tree definition, like so:

Demo

const projectTree = {
    $className: "Folder",
    NumItems: {
        $className: "IntValue",
        Data: "Folder", // This is a shorthand for { $className: "Folder" }
    },
} as const;

function g(o: EvaluateInstanceTree<typeof projectTree>) {
    return o.NumItems.Value++;
}

function f(o: Instance) {
    if (validateTree(o, projectTree)) {
        print(o.NumItems.Data.GetFullName()); // good
        g(o); // good!
    }
    o.NumItems.Data.GetFullName(); // error!
    g(o); // error!
}

The first parameter must be an Instance (or extend from it). The second parameter must be an object tree similar to ones considered valid by Rojo. Every tree must have a $className member, and can have any number of keys which represent the name of a child instance, which should have a corresponding value which is this same kind of tree. There is also a shorthand syntax, seen above with Folder: "Folder", which is equivalent to Folder: { $className: "Folder" }.

Note: Currently, the as const may be necessary to preserve the true type of the object tree. Your types will not work if you do not use the tree object in-line or declare it with as const after it.

This library also exports EvaluateInstanceTree if you want to use it for your own nefarious purposes.

Also see yield-for-tree