jQuery event.which

What Is event.which?

A Number property that tells you which key or which mouse button was pressed. Added in jQuery 1.1.3. It normalizes keyCode / charCode for keys, and reports 1 / 2 / 3 for left / middle / right mouse buttons.

event.which  // Number property — no parentheses

// Official keydown idea
$("#whichkey").on("keydown", function (event) {
  $("#log").html(event.type + ": " + event.which);
});

// Mouse: 1 = left, 2 = middle, 3 = right
// Keys: 13 = Enter, 27 = Escape (common codes)

How to Use event.which

Read it on the event object inside a keyboard or mouse handler.

1. Bind keydown (keys) or mousedown / mouseup (buttons).
2. Accept the event argument in the handler.
3. Read event.which (property — no ()).
4. Compare to a known code (13 Enter, 1 left button, …).
5. Optionally show event.type + ": " + event.which while learning.

Pseudocode

input.on("keydown", handler)
box.on("mousedown", handler)

when keydown fires:
    which = normalized key code
    log type + ": " + which

when mousedown fires:
    which = 1 (left) or 2 (middle) or 3 (right)
    log type + ": " + which

// Common key checks:
if which === 13 → Enter
if which === 27 → Escape

Cheat Sheet

Keep these codes handy while reading which.

Live Preview

Focus the input and press keys — same idea as the official jQuery API keydown demo. Or press a mouse button on the box below.

Waiting — type or click.

jQuery Examples

Short, copy-ready snippets. Open DevTools, or use Try It Yourself for a live editor.

$("#whichkey").on("keydown", function (event) {
  $("#log").html(event.type + ": " + event.which);
});

keydown: 65
keydown: 13

$("#whichkey").on("mousedown", function (event) {
  $("#log").html(event.type + ": " + event.which);
});

mousedown: 1
mousedown: 3

$("#name").on("keydown", function (event) {
  if (event.which === 13) {
    event.preventDefault();
    $("#out").text("Enter pressed — value: " + $(this).val());
  }
});

Enter pressed — value: hello

$("#panel").on("keydown", function (event) {
  if (event.which === 27) {
    $("#out").text("Escape — panel closed.");
  }
});

Escape — panel closed.

$("#box").on("mousedown", function (event) {
  var name = { 1: "left", 2: "middle", 3: "right" }[event.which]
    || "unknown";
  $("#out").text(event.type + ": " + event.which + " (" + name + ")");
});

mousedown: 1 (left)

Performance Notes

Reading which is free. Cost comes from work you do after the compare — keep shortcut handlers short.

Key Takeaways