Explain how client-side events like OnSuccess, OnFailure, and OnBegin work in an AJAX form.

Question

ICSM Computer · Answer

In ASP.NET MVC, when using 
Ajax.BeginForm, client-side events like OnBegin,
OnSuccess, and OnFailure let you hook into the AJAX request lifecycle so you can run JavaScript at specific moments during the request.
These events are part of the AjaxOptions object and are triggered
automatically by the 
jQuery Unobtrusive Ajax library.
AJAX Lifecycle Overview
OnBegin → before the request is sentOnSuccess → when a successful response is received (HTTP 200 OK)OnFailure → when the server returns an error (like 400/500), or AJAX failsOnComplete → after the AJAX call is finished (success or failure)
1. OnBegin
OnBegin = "onFormBegin" // function name
Triggered before the form is submitted.
You can use this to:
Show a loading spinnerValidate fields manuallyCancel submission by returning false
Example:
function onFormBegin() {
    console.log("Form is about to be submitted...");
    return true; // proceed
    // return false; // cancel AJAX request
}
2. OnSuccess
OnSuccess = "onFormSuccess" // function name
Triggered when the server returns a successful response (200 OK).
You can use this to:
Show a success messageUpdate the UIReset the form
Example:
function onFormSuccess(response) {
    console.log("Form submitted successfully.");
    $("#messageBox").text("Saved successfully!");
}
If the action returns HTML, it will also be inserted into the UpdateTargetId DOM element.
3. OnFailure
OnFailure = "onFormFailure" // function name
Triggered when:
The AJAX request fails (network/server issue)The action returns a non-success status (like 500 Internal Server Error)
Example:
function onFormFailure(xhr, status, error) {
    console.log("Failed:", error);
    $("#errorBox").text("An error occurred. Please try again.");
}
How to Wire These Up
@using (Ajax.BeginForm("SaveData", "Home", new AjaxOptions
{
    OnBegin = "onFormBegin",
    OnSuccess = "onFormSuccess",
    OnFailure = "onFormFailure",
    UpdateTargetId = "resultDiv"
}, new { @id = "myForm" }))
{
    @Html.TextBox("Name")
    andlt;input type="submit" value="Submit" /andgt;
}
Bonus: OnComplete
Not directly in AjaxOptions, but you can hook into global AJAX events:
$(document).ajaxComplete(function () {
    console.log("AJAX complete");
});
Notes
The handler names ("onFormSuccess") are just string names. Make sure those functions exist in JavaScript scope.Always check the rendered HTML to ensure data-ajax-* attributes are correctly output.

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Explain how client-side events like OnSuccess, OnFailure, and OnBegin work in an AJAX form.

ICSM Computer

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1 Answers

AJAX Lifecycle Overview

1. OnBegin

2. OnSuccess

3. OnFailure

How to Wire These Up

Bonus: OnComplete

Notes

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