How to access quantityInStock on a dynamic page

I have a dynamic product page and I want to access product quantity in stock with code.
I fount this in the documentation

$w('#myProductPage').getProduct()
  .then( (product) => {
    let productName = product.name;
    let productDescription = product.description;
    // see example product object below
  } )
  .catch( (error) => {
    console.log(error);
  } );

The only thing is that I don’t know whats the page name with what i have to replace ‘#myProductPage’.