Make `POST` from blogspot iframe to `doPost` from 'Apps Script'

Question

I created an iframe in the custom HTML of 'blogspot'.

In the src of the iframe there is the link to 'Apps Script' (https://script.google.com/macros/s/.../exec).

In the .gs of 'Apps Script', there is the doGet below:

function doGet() {
const html = HtmlService.createHtmlOutputFromFile("blogspot");
return html.setXFrameOptionsMode(HtmlService.XFrameOptionsMode.ALLOWALL);
}

The blogspot file is the HTML page of my blogger. I did this to avoid editing the HTML in blogger itself.

doGet is working correctly.

However, when I tried to do a POST using fetch inside the 'blogspot' HTML (iframe content), then I got the error below:

userCodeAppPanel:1 Access to fetch at 'https://script.google.com/macros/s/.../exec' from origin 'https://...-script.googleusercontent.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

I looked for other CORS resolutions here on the forum, but I didn't find what I'm looking for. How can I solve the problem?

• Patsytalk: Would you be able to provide your whole script, and also your expected output so that we can further help you.
• TheMaster: Use simple requests.

Answer 1

If you want to make a POST request to a Google Apps Script web application, it should include a doPost function

Example

function doPost(e){
 console.log(JSON.stringify(e, null, " ");
 return ContentService.createTextOutput('Hello world!')
}

Reference

• https://developers.google.com/apps-script/guides/web