Replace null values to empty values in a JSON OBJECT

Here's how you should be doing it, replacing the objects values with empty strings, not stringifying it

$.post("/profil_process/wall/preview-post.php",param, function (data){

    (function removeNull(o) {
        for(var key in o) {
            if( null === o[key] ) o[key] = '';
            if ( typeof o[key] === 'object' ) removeNull(o[key]);
        }
     })(data);

     $('#previewWall').html(
          getPostWall(
              data.type,
              data.titre,data.url,
              data.description,
              data.media,
              data.photo_auteur,
              data.nom_auteur,
              data.url_auteur,
              data.date_publication
          )  // ^^^ why not just pass the entire object ?
    ).fadeIn();

    $(".bouton-vertM").show();
    $("#wLoader").hide();

},'json');

If you can replace null-s with empty strings on serialized string, do something like this:

data = JSON.parse(JSON.stringify(data).replace(/\:null/gi, "\:\"\"")); 

Your function should be like this:

function (key, value) {
    return (value === null) ? "" : value;
}

If the value is null, then it returns an empty string.

For anyone still looking for a solution.

Used this in my angular 2 app to remove all null values returned by my db query.

Create an angular 2 function in the component

    replacer(i, val) {
     if ( val === null ) 
     { 
        return ""; // change null to empty string
     } else {
        return val; // return unchanged
     }
    }

Or Javascript function

    function replacer(i, val) {
     if ( val === null ) 
     { 
        return ""; // change null to empty string
     } else {
        return val; // return unchanged
     }
    }

Then use the function in JSON.stringify method

    JSON.stringify(result, this.replacer)