How to get keyboard value in JavaScript

JavaScript, as a language widely used in Web programming, can be used to implement user interaction functions. Getting the keyboard value is also a commonly used operation in JavaScript. In this article, we will explain how to get the keyboard value using JavaScript.

Keyboard events in JavaScript

In JavaScript, we can use keyboard events to capture keyboard input. There are three types of keyboard events: keydown, keypress and keyup.

1. keydown event: Triggered when the user presses any key on the keyboard, including special keys (such as Shift and Ctrl) and non-special keys (such as letters and numbers).
2. keypress event: Triggered when the user presses any key on the keyboard, but it only includes keys that can produce characters. Special keys do not generate keypress events.
3. keyup event: Triggered when the user releases any key on the keyboard.

Through these keyboard events, we can know which keys the user pressed on the keyboard, and we can obtain the key code value of the corresponding key.

The concept of key code value

The key code value refers to the numerical code transmitted from the keyboard input device to the computer. These codes represent a unique identifier for each key on the keyboard. Each keycode value has a unique ASCII code value that can represent the corresponding character.

JavaScript method of obtaining keyboard value

In JavaScript, we use the event.keyCode property to obtain the keyboard value. Use this property in the event handler to get the keyboard value in the keyboard event. The following is an example:

document.addEventListener("keydown", function(event) {
    alert(event.keyCode);
});

This code listens to a keydown event and uses the alert function to display the keyCode value when the event is triggered.

In addition, we can also use other related properties of the event object to obtain the keyboard value, such as:

1. event.key: represents the character corresponding to the pressed key, such as lowercase letters "a" or the number "3".
2. event.code: Indicates the physical location of the pressed key. For example, the code value of the "a" key is "KeyA", and the code value of the numeric key "3" is "Digit3".

It should be noted that the keyCode attribute is not supported in some browsers, while the key and code attributes are the new standard and can be used in most modern browsers.

Commonly used keyboard values

Commonly used keyboard values ​​include letters, numbers and special keys (such as Ctrl, Shift and Enter, etc.). The following are some common keyboard values ​​​​and their corresponding keyCode values:

• Letter and numeric keys: the keyCode value is the same as the ASCII code value. For example, the keyCode value of the a key is 97, and the keyCode value of the A key is 97. is 65, and the keyboard values ​​corresponding to the numbers 0-9 are 48-57 respectively.
• Special keys: The keyCode value of the Ctrl key is 17, the keyCode value of the Shift key is 16, the keyCode value of the Enter key is 13, and the keyCode value of the Tab key is 9.

Through these keyboard values, we can determine whether the user pressed a specific key and respond accordingly.

Summary

This article introduces how to get the keyboard value in JavaScript. Through the event handling function, we can capture keyboard events and obtain the corresponding keyboard values. Commonly used keyboard values ​​include letters, numbers, and special keys. Being familiar with these keyboard values ​​will help achieve better user interaction functions.

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