How to send a POST request from App Script to Firebase with an array

Question

I'm trying to send a POST request from an App Script application to a firebase cloud function. But I'm not being able to send correctly arrays inside this request. The request is sending the array in a messy way that the cloud function can't read it correctly

I'm using the following code:

    const data = {
      var1: 'string',
      var2: {name: 'object'},
      var3: new Date(),
      var4: [1, 2, 3],
      var5: [{name: 'any object'}, {name:  'inside an array'}],
    }

    const url = "https://us-central1-my-app.cloudfunctions.net/executeFunction";
  
    const options = {
      method: "post",
      "Content-Type": "application/json", //I tried to change this content-type for other options
      payload: data
    };

    const request = UrlFetchApp.fetch(url, options);

On the server side I tried to read the data using the following ways:

export const executeFunction = functions.https.onRequest(async(req, res) => {
  //option 1
  const data = JSON.parse(req.body);
  res.send(JSON.stringify(data));

  //option2
  const data = req.body;
  res.send(JSON.stringify(data);
})

But on the server the req.body returns me the following value:

{
  "var1":"string",
  "var2":{"name":"object"},
  "var3":"2020-07-14T18:45:21.946Z",
  "var4":[Ljava.lang.Object;@5e1b03dd, // :(
  "var5":[Ljava.lang.Object;@19d93f99  // :(

How can I get the array values correctly?

I suspect that it may be something related to the charset, but I already tried using "Content-Type": "application/json; charset=utf-8" on the options object and it didn't work.

Any ideas on how to solve it? :)

Update:

Thanks @Pickachu

I had to change 2 things: -stringify the payload -change the key on options from "Content-Type" to "contentType"

Here the code:

    const options = {
      method: "post",
      contentType: "application/json", //changed here
      payload: JSON.stringify(data) //and here
    };

    const request = UrlFetchApp.fetch(url, options);

Answer 1

You are almost getting it. A POST request from UrlFetcgApp with a json payload should have the payload serialized:

https://developers.google.com/apps-script/reference/url-fetch/url-fetch-app#fetch(String,Object)

const options = {
      ...
      payload: JSON.stringify(data)
    };

And a firebase cloud function using a https trigger automatically parses the json body so there is no need to parse or stringify it.

export const executeFunction = functions.https.onRequest(async(req, res) => {
  const data = req.body;
  console.log(data.var1);
  console.log(data.var2);
  console.log(data.var3);
})