如何在子页面的onload事件中调用JavaScript

Question

I have an ASP.net application with an aspx page.

In Page_Load event of the aspx page, I'm handling some code which is based on the value of a hidden variable from the javascript(assigning result of javascript to hidden variable).

I am calling the javascript in Page_Load of the child page, and in the immediate statement, I'm making use of the hidden variable value for processing. When I access hidden variable value, I'm getting default value only.

Please suggest me any of handling the scenario. I need to execute the javascript and get the result into the hidden variable. Both in need to occur in Page_Load event only.

Hidden Variable declaration:

<asp:HiddenField runat='server' ID='hdnDate' Value='0' />

Javscript:

function getCDate() {
    var nowDate    = new Date();  
    var curr_month = nowDate.getUTCMonth();
    curr_month ++;
    var dt = curr_month + "/" + nowDate.getUTCDate() + "/" +nowDate.getFullYear()+ " " + nowDate.getUTCHours()+":" +nowDate.getUTCMinutes()+":" +nowDate.getUTCSeconds();
    document.getElementById("ctl00_ContentPlaceHolder1_hdnDate").value = dt;          
    return true;
}

Page_Load method in code behind file:

protected void Page_Load(object sender, EventArgs e)
{
    Page.ClientScript.RegisterStartupScript(this.GetType(), "alert", "getCDate();", true);
    DateTime dt=Convert.ToDateTime(hdnDate.Value);
    dt.AddDays(10);    //getting error here because dt contains01/01/0001       
}

Answer 1

You cannot call javascript in Page_Load . It is client side thing so should come from browser only. You can check if page is postback using IsPostBack property of Page object like this:

if(IsPostBack)
{
   //this is coming from browser so you javascript  might have been
   //called and proper value set in hidden field.
}

Answer 2

Javascript is run on the client side, so can't run in the Page_Load event on the Server.

From the looks of your code, I'm pretty sure you don't need javascript, you can just put the value into a SessionVariable as:

Session.Add("DateRendered", DateTime.Now.AddDays(10).ToString("MM/dd/YYYY"));

And then retrieve it later. ASP.net takes care of storing it in the Request/Response.

Answer 3

RegisterStartupScript will register your block of script for the next page load. if you just want some value to be transferred to .cs page write a static method on the .cs and call it from javascript using PageMethods.MethodName();