PHP / Javascript variable passing -- unexpected results

Question

I am calling a php page (using PHP7.0) from javascript (on Chrome Version 67.0.3396.99). Reading around the web, I used a code example. Passing a json string through PUT to php is supposed to deliver a $_POST variable that is a map.

{"a":"A","b":"B","c":"C"} becomes

$_POST = [ "a" => "A", "b" => "B", "c"=>"C" ]

However, in my code below, javascript passed instead

$_POST = [ "{"a":"A","b":"B","c":"C"}" : "" ]

This is bizarre. If not a map, I would have expected a String

Did I do something wrong? This is a little nerve-wracking to think the code is unreliable for production. Or perhaps there is a better approach?

javascript:

function testeroo(){
 json_ = '{"a":"A","b":"B","c":"C"}'
 jQuery.ajax({
 type: "POST",
 url: './test.php',
 data: json_,
 success: function (obj) {
 alert(obj); 
 },
 error: function () {
 alert("ERROR testeroo");
 }
 });
}

test.php confirms this:

foreach ($_POST as $key => $value){
 $zeroKey = $key; 
 //only one key, so $zeroKey is only key
}
$j = json_decode($zeroKey);
 //$j is the expected map

Answer 1

your json_ is string, remove ''

 json_ = {"a":"A","b":"B","c":"C"}

Answer 2

two solutions:

1

as suggested by the other user:

remove '' from your json string

2

if you want to use a string you must also use the function JSON.parse()

Example

 var json_= '{"a":"A","b":"B","c":"C"}';
 json_= JSON.parse(json_);