In this article I will explain with an example, how to persist
JavaScript variables and objects across PostBack in ASP.Net.
HTML Markup
The HTML Markup consists of following controls and elements:
Controls
The Button has been assigned with an OnClientClick event handler.
Elements
SPAN – For displaying preserved values.
HiddenField – For storing values.
C#
<span id="array_display"></span>
<br />
<asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClientClick="UpdateArray()" />
<input type="hidden" id="array_store" name="ArrayStore" value='<%=this.ArrayStore %>' />
VB.Net
<span id="array_display"></span>
<br />
<asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClientClick="UpdateArray()" />
<input type="hidden" id="array_store" name="ArrayStore" value='<%= Me.ArrayStore %>' />
Persisting JavaScript variables and objects across PostBack
First, the variable is declared.
Inside the
JavaScript window.onload event handler, the contents of the
HiddenField is displayed in HTML SPAN.
UpdateArray
When the
Submit Button is clicked, the
JavaScript UpdateArray function is called. Then, a variable is created and a check is performed if Array is empty. If found empty, then a new Array object is created if not empty, then it is separated by comma (,).
After that, the push method is called where an Array is passed with adding 1 as parameter to it.
The join method is called where we pass comma (,) to it and then, it stored inside the value.
<script type="text/javascript">
var array_store;
window.onload = function () {
array_store = document.getElementById("array_store");
document.getElementById("array_display").innerHTML = array_store.value;
};
function UpdateArray() {
var arr;
if (array_store.value == "") {
arr = new Array();
} else {
arr = array_store.value.split(",");
}
arr.push((arr.length + 1).toString());
array_store.value = arr.join(",");
};
</script>
Updating Array using C# and VB.Net
First the string variable is created and empty value is stored inside it.
Inside the Page_Load event handler, the value of HiddenField is fetched from the Request.Form collection and set in the variable (created earlier).
C#
protected string ArrayStore = "";
protected void Page_Load(object sender, EventArgs e)
{
this.ArrayStore = Request.Form["ArrayStore"];
}
VB.Net
Protected ArrayStore As String = ""
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
Me.ArrayStore = Request.Form("ArrayStore")
End Sub
Screenshot
![Persist JavaScript variables and objects across PostBack in ASP.Net]()
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Demo
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