How to detect/track postback in javascript?

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猫巷女王i

How to detect/track/check postback in javascript(e.g in asp.net Page.isPostBack())? Any suggestion?

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11条回答

逝去的感伤

2020-12-02 19:44
on Page_Load on your server-side : The following uses an overload of RegisterClientScriptBlock() that will surround our string with the needed script tags

Server-Side
```
if (Page.IsPostBack){
   ClientScript.RegisterClientScriptBlock(GetType(),
            "IsPostBack", "var isPostBack = true;", true);
}
```
Then in your script which runs for the onLoad, check for the existence of that variable.
```
if (isPostBack){
   //do something here
}
```
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情书的邮戳

2020-12-02 19:45

This should work for ASP.Net pages without relying on a backend supplied variable/control:

function isPostBack(frmID) {
    var eventtarget = "";
    var eventargument = "";

    if (!!frmID) {
        if (document.forms.length == 0) return false;

        sForm = document.forms[0];
    }
    else {
        sForm = document.getElementById(frmID);

        if (!sForm) return false;
    }

    if (sForm.__EVENTTARGET) eventtarget = sForm.__EVENTTARGET.value;
    else return false;

    if (sForm.__EVENTARGUMENT) eventargument = sForm.__EVENTARGUMENT.value;
    else return false;

    if (eventtarget != "" || eventargument != "") return true;
    else return false;
}

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死守一世寂寞

2020-12-02 19:47
As JavaScript shouldn't be written with server-side code, and injecting new elements into the page seems like overkill, it seems to me that the simplest solution is to add [datat-*] attributes to the <head> element:
_{In Page_Load:}
```
Page.Header.Attributes["data-is-postback"] IsPostBack ? "true" : "false";
```
This can then be accessed as:
_jQuery:
```
$('head').data('isPostback');
```
_{Vanilla JS:}
```
document.head.getAttribute('data-is-postback') === 'true';
```
Of course, if you treat the [data-is-postback] attribute as a boolean attribute, you could alternatively use:
_{In Page_Load:}
```
if (IsPostBack)
{
    Page.Header.Attributes.Add("data-is-postback", "");
}
else
{
    Page.Header.Attributes.Remove("data-is-postback");
}
```
_jQuery:
```
$('head').is('[data-is-postback]');
```
_{Vanilla JS:}
```
document.head.hasAttribute('data-is-postback')
```
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别跟我提以往

2020-12-02 19:48

ASPX:

<input type="hidden" id="_ispostback" value="<%=Page.IsPostBack.ToString()%>" />

Client-side Script:

function isPostBack() { //function to check if page is a postback-ed one
  return document.getElementById('_ispostback').value == 'True';
}

PS: I have not tested it but I've done somthing similar before and it works.

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伪装坚强ぢ

2020-12-02 19:51

I have a solution that worked for me.

// Postback catch
var prm = Sys.WebForms.PageRequestManager.getInstance();
prm.add_endRequest(function (s, e) {
    alert("post back");
});

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