How to pass ASP.NET server side array to client side and binding them with Html element?

By | January 18, 2011

This is a very often requirement for an ASP.NET Developer to pass a sever side array to client side and access them through java Script. There are several ways to do that. But here I am describing one of the simplest steps to pass server side array to client side. In this blog post you will get to know two things, first one is the how to pass the array from server side to client side and second one is the how to bind that array to an empty “html dropdown” list.

Well, the easiest way to pass the server side array to a client side is using “RegisterArrayDeclaration” . RegisterArrayDeclaration method registers a javascript array with the System.Web.UI.Page Object. As the array object registered with the “Page” object so we can access it from javascript easily. RegisterArrayDeclaration takes array name and value of the array element as argument.

In below example, I have registered one array with name of “Skills”.

  protected void Page_Load(object sender, EventArgs e)
       // Register List of Languages
        Page.ClientScript.RegisterArrayDeclaration("Skills", "'C#'");
        Page.ClientScript.RegisterArrayDeclaration("Skills", "'VB.NET'");
        Page.ClientScript.RegisterArrayDeclaration("Skills", "'C'");
        Page.ClientScript.RegisterArrayDeclaration("Skills", "'C++'");

Now, what above declaration does? This is nothing but a declaration of a java script array like,

Var Skills = new Array('C#', 'VB.NET','C','C++');

These “Skills” array is now only a JavaScript array which is easily accessible by client side code. Now Let’s have a look how to access them and how to bind them in a dropdown list. In my form, I have an Html select element and one Html Button. I want my Server side ( Which is now a client side ) array to bind in the dropdown list.

  <select id="ddlNames" name="D1">
    </select><input id="BtnNameLoad" type="button" value="Load Name" onclick="return BtnNameLoad_onclick()" />

Below is the code snippet for bind the array to html control.

function BtnNameLoad_onclick() {

            //Get The Control ID for the dropdown
            var listID = document.getElementById("ddlNames");
            //Check if the object is not null
            if (listID != null) {
                for (var i = 0; i < Skills.length; i++) {
                   // Create and Element Object of type "option"
                    var opt = document.createElement("option");
                    //Add the option element to the select item
                    //Reading Element From Array
                    opt.text = Skills[i];

In the above code snippet, I have read the skills name using Skills[i] . which was actually registered from server side. Another interesting thing is to bindng the array elements in “Select” item. As we all know, “Option” tag element is the placeholder for the select content. So I have created one “Option” element using “createElement

    var opt = document.createElement("option");

This opt object is nothing but the place holder for item of the this “Select” element. So for every element I have created an object for “option” element and added them in to the actual list by reading the value from array.

You can also check the array elements that are registred through debugging

Below is the sample output:

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