Passing parameter to a JavaScript function as a Dictionary object

Question

Please, help me to understand the following part of the code from the post http://stackoverflow.com/questions/133925/javascript-post-request-like-a-form-submit/133997#133997

function post_to_url(path, params, method) {
....
for(var key in params) {
    var hiddenField = document.createElement("input");
    hiddenField.setAttribute("type", "hidden");
    hiddenField.setAttribute("name", key);
    hiddenField.setAttribute("value", params[key]);

    form.appendChild(hiddenField);
}
....

Does this mean that we could pass the Dictionary object to the JavaScript function (calling JavaScript function from Silverlight app) and it will generate the param string in the form of key=value&key2=value2&key3=value3 ?

For example, passing the following Dictionary:

Dictionary<string, decimal> postdata = new Dictionary<string, decimal>();
postdata["productID1"] = 126504;
postdata["productID2"] = 126505;

We get the function output: productId1=126504&productId2=126505 ?

Answer 1

Depends what you mean by output. The function does not output anything directly. It creates a form and adds an input element for every key-value pair in the object. It then submits that form, and the browser internally generates that parameter string and POSTs it to the URL. If by output you mean "posts to the server," then yes - that is what it does.

Regarding passing in objects from managed code (silverlight), it seems it is possible. Dictionarys will be marshalled to Javascript objects as long as the key is a string. You will be able to access the entries by using the regular javascript property notation (dictionary["key"] or dictionary.key).

More reading regarding Dictionary marshalling.

Also, I may be wrong (my C# is a bit rusty), but wouldn't:

Dictionary<string, decimal> postdata = new Dictionary<string, decimal>();
postdata["productID"] = 126504;
postdata["productID"] = 126505;

be considered invalid? In Dictionarys, like Javascript Objects, all keys must be distinct, no?

---

If you just want the query string, coming up with a function to create a parameter/query string from a JS object is relatively easy.

For example:

function paramString(object) {
    var strBuilder = [];
    for (var key in object) if (object.hasOwnProperty(key)) {
       strBuilder.push(encodeURIComponent(key)+'='+encodeURIComponent(object[key]));
    }
    return strBuilder.join('&');
}

paramString(postdata)
"productID1=126504&productID2=126505"

Answer 2

Every java-script object is implemented as a dictionary - all properties are name-value pairs. So to pass dictionary to post_to_url function, you can use

var postdata = {};
postdata["name1"] = value1;
postdata["name2"] = value2;
...

post_to_url(url, postdata, "post"

Note that syntax postdata["name1"] and postdata.name1 are equivalent - they refer to same value. You can also use alternate syntax using JS object notation. For example,

var postdata = {
    "name1" = value1,
    "name2" = value2,
    ...
    "namex" = valuex
};

post_to_url(url, postdata, "post"

Now to answer another part of your question - the sighted JS function will only post the data from params. It will not create a url such as productId=126504&productId=126505 for GET method. For that, you need to roll up your own version such as

function post_to_url(path, params, method) {
    method = method || "post"; // Set method to post by default, if not specified.
// The rest of this code assumes you are not using a library.
// It can be made less wordy if you use one.
var form = document.createElement("form");
form.setAttribute("method", method);
form.setAttribute("action", path);

for(var key in params) {

    if (method.toUpperCase() === "GET") {
       if(path.indexOf("?") < 0) {
           path += "?";
       }
       path += "&" + key + "=" + params["key"];
    }
    else {

       var hiddenField = document.createElement("input");
       hiddenField.setAttribute("type", "hidden");
       hiddenField.setAttribute("name", key);
       hiddenField.setAttribute("value", params[key]);

       form.appendChild(hiddenField);
    }
}

document.body.appendChild(form);    // Not entirely sure if this is necessary
form.submit();

}