How to read array passed to php in async call - php

Question

I have the following in a js script:
let skippers = {};
for(let i = 0; i < skipperIds.length;i++){
skippers[skipperIds[i].value] = skipperIds[i].checked;
}
regData.skippers = skippers;
responseData = sendData2('https://sailwbob.com/lagin/public/register.php',regData);
where sendData2 is an async call using axios. skippers looks like
{1:true,20:false}
In my php file I have:
$skippers = ($_POST['skippers']);
$skipperIds = array_keys($skippers);
$skipperValues = array_values($skippers);
but this is not working. I think php converts an array in $_POST to a string but I'm not sure.
two qustions:
how do I convert $skippers back to an array?
I've been trying to use print_r to see the data on the server but as this is an async call it's not working as the print_r results are being sent back to the js script and not printing out on the screen. Is there a way to see the results of print_r?
Update:
I tried $x=json_decode($_POST); but got an error saying it was expecting a string.
here's the call to axios:
function sendData2(url,emailPass){
let bodyFormData = new FormData()
for (const [key, value] of Object.entries(emailPass)) {
//console.log(key,value)
bodyFormData.append(key,value)
}
return axios({
method: 'POST',
url: url,
data: bodyFormData,
headers: {'Content-Type': 'multipart/form-data'}
})
.then(function(response){
return response.data
})
.catch(function(response){
return response
})
}
update2:
$skippers shows $skippers = [object Object]. Is there a way to send this to the server correctly?

Answer 1

As discussed in this article, axios serializes Javascript objects to JSON and becase PHP doesn't support JSON as a data format for populating $_POST, you can retrieve them in PHP like this:
$_POST = json_decode(file_get_contents("php://input"),true);
$skippers = $_POST['skippers'];

Answer 2

While axios does automatically stringify data it apparently doesn't do that for nested arrays. I needed to add:
regData.skippers = JSON.stringify(skippers); in my js
and then in the php file
$skippers = get_object_vars(json_decode($_POST['skippers']));