whichEvent Property

事件对象参考手册 Event Object

Examples

Get the Unicode value of the pressed keyboard key:

var x = event.which;

xThe output result is:

119 // 119 is the character "w"

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More examples are included at the bottom of this article.

Definition and Usage

The which property returnsonkeypressthe character code of the key that triggered the event, oronkeydownoronkeyupthe key code of the key.

The difference between the two types of codes is:

Character code - a number representing an ASCII character
Keyboard code - a number representing the actual key on the keyboard

Both types of values are not always equal. For example, the lowercase character "w" and the uppercase character "W" have the same keyboard code (the "W" code is "87"), but they have different character codes. The two characters produce different output (the character codes for "w" and "W" are "119" and "87") - see the examples below for a better understanding.

Tip:If you need to know whether the user pressed a printing key (such as "a" or "5"), it is recommended to use the onkeypress event. If you need to know whether the user pressed a function key (such as "F1", "CAPS LOCK" or "Home"), you can use the onkeydown or onkeyup event.

Note:IE8 and earlier versions do not support the which property. Browsers that do not support it can use thekeyCodeproperty. However, the keyCode property is invalid in the onkeypress event in Firefox. To be compatible with these browsers, you can use the following code:

var x = event.which || event.keyCode; // UsewhichorkeyCode, this supports different browsers

Tip:For a list of all Unicode characters, see ourComplete Unicode Reference Manual。

Tip:If you need to convert a Unicode value to a character, you can use thefromCharCode()method.

Note:This property is read-only.

Note:The which and keyCode properties provide a method for browser compatibility. For the latest version of DOM events, it is recommended to use thekeyproperty to replace this method.

Tip:If you want to check whether the "ALT", "CTRL", "META" or "SHIFT" key is pressed, you can use thealtKey, ctrlKey, metaKeyorshiftKeyproperty.

Browser Support

The numbers in the table specify the first browser version that fully supports the property.

Property
which	Yes	9.0	Yes	Yes	Yes

Syntax

event.which

Technical Details

Return Value:	A number, representing a Unicode character code or a Unicode key code
DOM Version:	DOM Level 2 Events

More Examples

Examples

Use onkeypress and onkeydown to demonstrate the difference between character code and keyboard code:

<input type="text" onkeypress="uniCharCode(event)" onkeydown="uniKeyCode(event)">

function uniCharCode(event) {
    var char = event.which || event.keyCode; // event.keyCode is used for IE8 and earlier versions
    document.getElementById("demo").innerHTML = "Unicode CHARACTER code: " + char;
}

function uniKeyCode(event) {
    var key = event.which || event.keyCode; // event.keyCode is used for IE8 and earlier versions
    document.getElementById("demo2").innerHTML = "Unicode KEY code: " + key;
}

When the "a" key is pressed on the keyboard (without Caps Lock), the output is as follows:

Unicode character code: 97
Unicode keyboard code: 65

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Examples

If the Esc key is pressed, pop up an alert message:

<input type="text" onkeydown="myFunction(event)">

function myFunction(event) {
    var x = event.which || event.keyCode; // event.keyCode is used for IE8 and earlier versions
    if (x == 27) { // 27 is the ESC key
        alert ("You pressed the Escape key!");
    }
}

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