jQuery .ajaxSend() Method

What Is .ajaxSend()?

.ajaxSend(handler) is jQuery’s legacy shorthand (since 1.0) for binding a global Ajax “about to send” handler on document. It runs just before every qualifying request leaves the browser. Internally it is sugar for .on("ajaxSend", handler).

// Deprecated (since 3.5)
$(document).ajaxSend(function (event, jqXHR, ajaxOptions) {
  // runs just before every qualifying Ajax request is sent
});

// Modern replacement
$(document).on("ajaxSend", handler);

// Bind only — no no-arg .ajaxSend() trigger form
// Opt out: $.ajax({ url: "/x", global: false })

How to Use .ajaxSend()

Recognize the legacy call, know its three handler arguments, and migrate to .on() / .off().

1. Attach the handler to document with .ajaxSend(handler) (legacy) or .on("ajaxSend", handler) (preferred).
2. Make requests with $.ajax(), $.get(), $.post(), or .load().
3. Optionally filter with ajaxOptions.url (response is not available yet).
4. Remove with .off("ajaxSend", handler) — not .unbind().
5. Use global: false on requests that must stay silent.

Pseudocode

call $(document).ajaxSend(handler)
    → internally: $(document).on("ajaxSend", handler)

when a jQuery Ajax request is about to be sent:
    if request.global === false:
        do not fire ajaxSend
        return

    fire ajaxSend
        for each registered handler:
            call handler(event, jqXHR, ajaxOptions)

    send the HTTP request
    // response is not available yet

to migrate:
    replace .ajaxSend(fn) with .on("ajaxSend", fn)
    remove with .off("ajaxSend", fn)

Cheat Sheet

Quick map from legacy shorthand to modern APIs.

Live Preview

Run a real $.get() and watch the legacy .ajaxSend() handler update the log before the request leaves.

Ready — pick an action and click Run.

jQuery Examples

Short, copy-ready snippets using the legacy shorthand. Prefer .on("ajaxSend") for new projects.

$(document).ajaxSend(function () {
  $(".log").text("Handler ran via .ajaxSend(function(){ ... }).");
});

$("#fetch").on("click", function () {
  $.get("https://jsonplaceholder.typicode.com/posts/1");
});

Click #fetch → $.get() starts
Before request leaves → .log shows
"Handler ran via .ajaxSend(function(){ ... })."

var targetUrl = "https://jsonplaceholder.typicode.com/posts/1";

$(document).ajaxSend(function (event, jqXHR, settings) {
  if (settings.url === targetUrl) {
    $(".log").text("About to send: " + settings.url);
  }
});

Matching URL → log shows "About to send: …"
Other URLs → handler runs, if-block skipped

$(document).ajaxSend(function (event, request, settings) {
  $("#msg").append(" Starting request at " + settings.url + " ");
});

Each outgoing request →
#msg gains " Starting request at URL "

Three parallel calls → three appends before responses

// Legacy — deprecated since jQuery 3.5
$(document).ajaxSend(function () {
  $("#out").text("Legacy: .ajaxSend(function(){ ... }).");
});

// Modern — use for new code
$(document).on("ajaxSend", function () {
  $("#out").text("Modern: .on('ajaxSend', function(){ ... }).");
});

Both handlers fire when $.get() starts
Behavior is identical — only the API name differs
Prefer .on("ajaxSend") for new code

var count = 0;

function onSend() {
  count++;
  $(".log").text("Handler active — ajaxSend count: " + count);
}

$(document).ajaxSend(onSend);

$("#remove").on("click", function () {
  $(document).off("ajaxSend", onSend);
  $(".log").text("Handler removed — count stays " + count + ".");
});

Run $.get() → count increments
Click Remove → .off("ajaxSend", onSend)
Next $.get() → handler no longer runs

Performance Notes

Legacy and modern binds have the same cost. Keep handlers light, filter by URL before touching the DOM, and prefer beforeSend for request-specific work.

Key Takeaways