file_get_contents(php://input) - gets the raw POST data and you need to use this when you write APIs and need XML/JSON/... input that cannot be decoded to $_POST by PHP some example :
send by post JSON string
<input type="button" value= "click" onclick="fn()">
<script>
function fn(){
var js_obj = {plugin: 'jquery-json', version: 2.3};
var encoded = JSON.stringify( js_obj );
var data= encoded
$.ajax({
type: "POST",
url: '1.php',
data: data,
success: function(data){
console.log(data);
}
});
}
</script>
1.php
//print_r($_POST); //empty!!! don't work ...
var_dump( file_get_contents('php://input'));