Merkle Tree js library won't load

We are trying to work with the merkle tree js library and compute proofs on-the-fly.

However, the library won't load.

"react-scripts": "4.0.3",
babel-loader: 8.1.0

Module parse failed: Unexpected token (86:49)
File was processed with these loaders:
 * ./node_modules/babel-loader/lib/index.js
You may need an additional loader to handle the result of these loaders.
|   }
|   leafLookup(leaf) {
Failed to compile.
Failed to compile.
Failed to compile.
OZ library crashes the app

How are you importing the library? Can you provide a repository that reproduces the problem?