How to use the matrix-js-sdk.User function in matrix-js-sdk

getUserByAccount(account) {
        if (account.startsWith('matrix-account:'))
            account = account.substring('matrix-account:'.length);
        return Q(new MatrixUser(this.client.getUser(account) || new Matrix.User(account)));
    }

_loadUser(userId) {
        var data = this._store.getItem("user_" + userId);
        if (!data) return null;

        var obj = JSON.parse(data);
        var presenceEvent = obj.presence ? new MatrixEvent(obj.presence) : null;
        var displayName = obj.displayName;
        var avatarUrl = obj.avatarUrl;

        var user = new User(userId);
        if (presenceEvent)
            user.setPresenceEvent(presenceEvent);
        if (displayName)
            user.setDisplayName(displayName);
        if (avatarUrl)
            user.setAvatarUrl(avatarUrl);

        this._registerUserListeners(user);

        return user;
    }