As question, I tried to use "useState" hook shown in the search_bar.js provided in the source code. But it gives me this error: 

web.assets_backend.min.js:14814 Uncaught SyntaxError: Cannot use import statement outside a module
web.assets_common.min.js:29 warning: Some modules could not be started
web.assets_common.min.js:29 Missing dependencies: Array(26)
web.assets_common.min.js:34 Non loaded modules: Array(58)

Part of the source code: 

import { useState } from"@odoo/owl";
odoo.define("myModel.TreeModel", function (require) {