How to convert if else shorthand to normal if else case

Below code, I update the react hook with if-else shorthand condition. To understand exactly this, I try to write it in normal if-else condition, but I couldn't. What is the equal case of this shorthand conditions?

This is working code.

const [array, setArray] = useState([]);

function addProduct(product){
  const ProductExist = array.find((item) => item.id === product.id);
  setArray(
   array.map((item) =>
   item.id === product.id
   ? { ...ProductExist, quantity: ProductExist.quantity + 1 }
   : item
   )
 );
}

This is my try according to the solutions of other topics. But it gives error.

setTestArray(array.map((item) => {
  return if(item.id === product.id){
   return { ...ProductExist, quantity: ProductExist.quantity + 1 }
  }else{
   return item
  }
}