how javascript submission function handles Checkbox in html form on google apps script?

In html data entry form, wanted to replace a Radio type with Checkbox for possible multi-selections:

<form id="ProductDetails" onsubmit="handleFormSubmit(this)">
  <p class="h4 mb-4 text-center">Restaurant Details</p>
  <div id="message"></div>
  <input type="text" id="recId" name="recId" value="" style="display: none">

  <div class="mb-1">
    <label for="name" class="form-label">Name</label>
    <input type="text" id="name" name="name" class="form-control form-control-sm" required>
  </div>

  <div class="mb-1">  //Text type
    <label for="name" class="form-label">Product Condition</label>
    <input type="text" id="name" name="name" class="form-control form-control-sm" required>
  </div>

  <div class="mb-1">
    <label class="form-label"><B>Product Condition</B></label><br>
    <div class="form-check form-check-inline">
      <input type="checkbox" id="new1" name="prodCondition" class="form-check-input" value="new1">
      <label for="new1" class="form-check-label">New1</label>
    </div>
    <div class="form-check form-check-inline">
      <input type="checkbox" id="new2" name="prodCondition" class="form-check-input" value="new2">
      <label for="new2" class="form-check-label">New2</label>
    </div>
  </div>

  <button type="submit" class="btn btn-primary">Submit</button>
</form>

//HANDLE FORM SUBMISSION, original that works
  function handleFormSubmit(formObject) {
    $('#spinnerModal').modal('show');
    google.script.run.withSuccessHandler(createTable).processForm(formObject);
    document.getElementById("ProductDetails").reset();
  }

The new submission function should include multi-selections from the Checkbox to its corresponding column/cel (hope separated with comma) in Google sheet. ChatGDP suggested this but it doesn’t work:

function handleFormSubmit(formObject) {
    // Initialize formObject.prodCondition as an array if it doesn't exist or isn't an array
    if (!Array.isArray(formObject.prodCondition)) {
        formObject.prodCondition = [];
    }
    
    console.log("Before collecting checkbox values:");
    console.log("prodCondition array length:", formObject.prodCondition.length);

    // Loop through all checked checkboxes and push their values into the array
    document.querySelectorAll('input[name="prodCondition"]:checked').forEach((checkbox) => {
        formObject.prodCondition.push(checkbox.value);
    });
    
    console.log("After collecting checkbox values:");
    console.log("prodCondition array length:", formObject.prodCondition.length);

    // Now that we've collected the checkbox values, we can proceed with the form submission
    console.log("Submitting form with the following values:");
    console.log(formObject); // Log the entire formObject to see its contents
    
    $('#spinnerModal').modal('show');
    google.script.run.withSuccessHandler(createTable).processForm(formObject);
    document.getElementById("ProductDetails").reset();
}

error from Console:

Before collecting checkbox values:
userCodeAppPanel:60 prodCondition array length: 2
userCodeAppPanel:64 Uncaught TypeError: formObject.prodCondition.push is not a function
    at userCodeAppPanel:64:34
    at NodeList.forEach (<anonymous>)
    at handleFormSubmit (userCodeAppPanel:63:70)
    at HTMLFormElement.onsubmit (userCodeAppPanel:1:8911)

Thanks for help. – Ben

tried ChatGDP but its solution didn’t work