Adding object to array also adds 'null' - php

Question

I send the following data to my php file via ajax:
JSON.stringify({test1: '1', test2: '2'})
I would like to write this data to my JSON FILE content.json containing an empty array
[]
I only want to add the content though if it is not there, yet. This is my PHP code:
$jsonStringObject = file_get_contents("php://input");
$phpObject = json_decode($jsonStringObject);
$newJsonStringObject = json_encode($phpObject);
header('Content-Type: application/json');
$jsonString = file_get_contents('content.json');
$data = (array) json_decode($jsonString, true);
if (in_array($phpObject, $data) === false){
$data[] = $phpObject;
}
$newJsonString = json_encode($data);
file_put_contents('content.json', $newJsonString);
It almost works. Something is wrong with the way the data is added to the array because when I call the function for the first time, it updates content.json to
[null,{"test1":"1","test2":"2"}]
On calling the function again, it adds the object again despite the if-statement:
[null,{"test1":"1","test2":"2"},{"test1":"1","test2":"2"},{"test1":"1","test2":"2"}]
Can anyone help me to spot the mistake?

Answer 1

You're comparing apples and oranges (or rather objects to arrays).
Make sure you decode all json as arrays:
$jsonStringObject = file_get_contents("php://input");
// Added true as second argument to get it bas as an array
$phpObject = json_decode($jsonStringObject, true);
$jsonString = file_get_contents('content.json');
// Removed the (array) since the second argument literally means "return as array"
$data = json_decode($jsonString, true);
if (in_array($phpObject, $data) === false){
$data[] = $phpObject;
}
$newJsonString = json_encode($data);
file_put_contents('content.json', $newJsonString);
Demo: https://3v4l.org/rnCn5