php - json return null value after POST -

a.php

$(document).ready(function() {     $("#submit_form").on("click",function(){         var json_hist =  <?php echo $json_history; ?>;         $.ajax({             type: "post",             url: "b.php",             data: "hist_json="+json.stringify(json_hist),             //contenttype: "application/json; charset=utf-8",             datatype: "json",             success: function(data){alert(data);},             failure: function(errmsg) {                 alert(errmsg);             }         });       });  }) 

b.php

$obj=json_decode($_post["hist_json"]); var_dump($_post); 

if comment contenttype: "application/json; charset=utf-8" everything's works fine if uncomment this. var dump return null.

when set contenttype in ajax, setting contenttype request not response.

it fails json contenttype because data you're sending key/value formatted data (which missing encoding) , data doesn't match contenttype. json contenttype header when you're sending raw json no identifiers, in case have identifier hist_json=.

i suggest changing to:

data: { hist_json : json.stringify(json_hist) }, 

using object hits_json key mean jquery safely url encode json , allow php pick $_post['hits_json'].

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if want use json contenttype have change ajax to:

data: { json.stringify(json_hist) }, // <-- no identifier 

and php:

$obj = json_decode($http_raw_post_data); var_dump($obj);