How to send data to json file using jquery/ajax

Question

I have found countless tutorials on how to retrieve data from json files using jQuery and ajax but none on how to POST data to a json file. If some one could show me or send me a small script on how to do this that would be great. I have searched everywhere on how to do this and have had no luck. I have seen examples of people doing it but they seem to forget to share important info that i am not seeing.I have no problem retrieving data json files using ajax. If someone could tell me if i am forgetting something or doing something wrong that would be great. I would be very appreciative if someone could send me a working file so that i can reverse engineer ir and understand how to do it. I am wanting to send the values from $firstName and $caption to the json file. I know this may seem stupid to others but i am tired of all the searching and not getting any straight answers.

Here is what i have.

      getImages: function(){
        var $firstName = $(".name"),
            $caption = $(".caption");
        var object = {
            name: $firstName.val(),
            caption: $caption.val()
        }
        $.ajax({
            type: 'POST',
            data: object,
            url: 'images.json',
            success: function(data){
                console.log("KILLER");
                var count = 0;
                $.each(data, function(i, imgSlide){
                    count ++;
                    //console.log(result.sliderImages[i].url[0].thumb);
                    var imageEl = "<img src='"+imgSlide.url[0].thumb+"' alt='"+imgSlide.name+"'>";
                    var slide = "<li class='imageSlide' data-id='"+count+"'>"+imageEl+"</li>";
                    $("ul.imageGallery").append(slide).fadeIn();
                });
            },
            error: function(){
                console.log("Abort");
            },
            timeout: 3000,
            beforeSend: function(){

            },
            complete: function(){

            }
        });

    }

and here is my JSON file

    [{
      "name": "Bootcamp",
      "url": [{
        "thumb": "img/ill-bootcamp.jpg",
        "med": "img/ill-bootcamp.jpg",
        "large": "img/ill-bootcamp.jpg"
            }],
      "caption": "Lifetime Fitness",
      "ID": ""
     },
     {
       "name": "Pinup Girl",
       "url": [{
            "thumb": "img/ill-pinup.jpg",
            "med": "img/ill-pinup.jpg",
            "large": "img/ill-pinup.jpg"
             }],
      "caption": "Illustration",
      "ID": ""
     },
     {
       "name": "SixDitch",
       "url": [{
             "thumb": "img/web-sixditch.jpg",
             "med": "img/web-sixditch.jpg",
             "large": "img/web-sixditch.jpg"
             }],
       "caption": "SD MotorSports",
       "ID": ""
     }]

Answer 1

It was a bit unclear ...
client side languages are not able to write or edit something on the server
via AJAX (with or without jQuery) you are only able to read data or send them
so you can pass your data to a php file then execute what you want to do , by php.
here is a tutorial for working with files in php
http://www.w3schools.com/php/php_file_open.asp
and here is another one for getting passed data by AJAX in php file
http://www.w3schools.com/php/php_superglobals.asp
look at $_GET , $_POST , $_REQUEST
good luck

Answer 2

So you will need to use server-side script language. In this case we will use PHP.

After defining your json object you turn it into string and send it to the php file via post. From there the PHP will take it and encode it as a JSON object. This json object will saved to a file named my_json_data.json with the php function file_put_contents(). If you want to append the new content instead of replacing the old one use the function like this:

file_put_content('my_json_data.json', $jsonObject, FILE_APPEND);

JavaSrcipt:

var $firstName = $(".name"),
    $caption = $(".caption");
var object = {
    name: $firstName.val(),
    caption: $caption.val()
}

var params = JSON.stringify(object);

$.ajax({
    type: 'POST',
    data: params,
    url: 'save_to_json.php',
    success: function(data){
        // do something on success
    },
    error: function(){
        // do something on error
    }
});

PHP (save_to_json.php):

    if (!isset($_POST['params']) && !empty($_POST['params'])) {
        $params = $_POST['params'];

        $jsonObject = json_encode($params);
        file_put_contents('my_json_data.json', $jsonObject);
    }

I hope I didn't missed something. Good luck.