Use external file js in robot-framework

I have a file js in my project

export function myFunction(parametro) {
  return "This is result  " + param;
}

and my file .robot

*** Settings ***
Library    SeleniumLibrary

*** Test Cases ***
Carregar Funções JavaScript
    Open Browser    https://google.com    Firefox
    Execute JavaScript    var script = document.createElement('script');
    ...    script.src = '/external-libs/robot-shared-function/index.js';
    ...    document.head.appendChild(script);

Usar Função JavaScript
    ${resultado}=    Execute JavaScript    return minhaFuncaoGlobal('algumParâmetro');
    Log    ${resultado}

But in results I have :

Usar Função JavaScript                                                | FAIL |
JavascriptException: Message: ReferenceError: myFunction is not defined
------------------------------------------------------------------------------
Teste-Lib                                                             | FAIL |
2 tests, 1 passed, 1 failed

I would like know how to use external function of file js