How to export variable data to a JSON file on the server using JavaScript/PHP?

Question

So let's say I have a HTML page and an input box on it. The user will type something in it, then I'll store it as a variable in JS, and then, can I somehow write the data of that variable to an already existing JSON file on the server?

How can I achieve this using JavaScript and/or PHP?

EDIT: I actually want to know how to write the data of a PHP variable to a JSON file that is in the same directory as the PHP file.

Answer 1

file_put_contents("json_file.json",json_encode($array));

Result:

 {"key":"value","anotherkey":"anothervalue"}  

Note: file_put_contents function will overwrite your file!

Edit: appendable:

 $array = json_decode(file_get_contents("json_file.json"),true); \n$array['your_new_key'] = "your_new_value"; \nfile_put_contents("json_file.json",json_encode($array));