问无光ReferenceError PouchDB

EN

   function pouchdb() {
        var db = new PouchDB("todos");

        var remoteDB = new PouchDB("http://example.cloudant.com/example");
        window.PouchDB = db;
        var doc = {
        "_id": "Can123",
        "name": "You123",
        "occupation": "See1",
        "age": 3,
        "hobbies": [
          "Watch 9pm show",
          "chasing laser pointers",
          "lookin' hella cute"
        ]
    };

    db.put(doc);        
PouchDB.sync(db, remoteDB);

}

<button onclick="pouchdb()">pouchdb</button>

function pouchdb() {
    var db = new PouchDB("todos");

    var remoteDB = new PouchDB("http://example.cloudant.com/example");
    var todo = {
        _id: "mittens1233",
        title: "hello",
        occupation: "kitten123"
    };
    db.put(todo, function callback(err, result) {
        if (!err) {
            console.log('Successfully posted a todo!');
        }
    });
}