How does a javascript program obtain the phone key value?

With the popularity of smartphones in people’s lives, more and more websites and applications are beginning to adapt to mobile devices. On the mobile terminal, the user's input method is also different from that on traditional computers. One of the significant differences is the input method. For web pages and applications, how to handle user input and obtain correct key values ​​on mobile devices has become an important issue.

JavaScript is a commonly used programming language that is widely used in front-end applications. In the mobile HTML5 development process, most user input needs to be processed and filtered. Therefore, learning how to obtain keyboard input on mobile devices becomes an important task.

Generally speaking, on computers, we will obtain user input information through event listening. To obtain the user's keyboard input information on mobile devices, we can use the following methods:

1. KeyboardEvent

In desktop browsers, we can usually use Keyboard event monitoring is used to obtain the user's key values, such as characters or function keys on the keyboard. Similarly, on mobile devices, we can also achieve it in a similar way.

In JavaScript, there is an event listener on the Window object, namely "keydown", which can return the value of the pressed key. We can use this event to monitor the user's keystrokes on the mobile device. .

window.addEventListener('keydown', function(event) {
  console.log(event.key);
});

When the user presses a key on the mobile device, this event is triggered and the value of the pressed key is output to the console. This value can be easily used for various logical judgments and data processing.

However, in some cases, we may need to obtain more key value information. It should be noted that the keyboard event objects on mobile devices are different from those in desktop browsers. On mobile devices, the keyboard event object contains more properties, such as whether the Alt, Shift or Ctrl key was pressed, whether a function key was pressed, etc.

So, if we need to obtain these additional key value information, we can use other properties provided by the keyboard event object. For example, we can use the code attribute to get the key code corresponding to the key:

window.addEventListener('keydown', function(event) {
  console.log(event.code);
});

After using this code, we can see the key code of the pressed key in the information output by the console. This key code is a number that represents the virtual key value corresponding to the pressed key. This value is unique across keyboards and is independent of the user's input language and keyboard layout.

In addition, we can also use other properties of KeyEvent to obtain other keyboard event information. For example, we can use event.key to get the characters corresponding to the keyboard event:

window.addEventListener('keydown', function(event) {
  console.log(event.key);
});

On mobile devices, the keyboard event object may return different characters depending on the user's input method and the current locale. So to get the correct character we have to get it using the event.key property.

2. Input event

In addition to using keyboard events, we can also use input events to monitor user input on mobile devices. Unlike keyboard events, input events can be used to monitor any user input, including handwriting and voice input.

var inputElement = document.getElementById('input-element');

inputElement.addEventListener('input', function(event) {
  console.log(event.target.value);
});

This code uses the input event to monitor the input of the input element and output the value entered by the user on the console. In the event handler function, we can use event.target to obtain the element object being entered to obtain the value of the input box.

It should be noted that input events on iOS and Android are slightly different. On iOS, the input event is not fired until the input is complete. On Android, the input event may be triggered when the user inputs.

3. Touch Event

Another way to get user input on a mobile device is to use the Touch event. Touch events are event types specifically designed to monitor touch operations on mobile devices. If your website or application needs to support gesture input and touch operations, then using Touch events is a good way.

In JavaScript, you can use the touchstart and touchend events to obtain the press and release operations when the user touches the input device with their fingers. If you need to detect that the user is performing a long press, you can use the touchmove event to capture the user's operation and determine whether the finger is in the same position (this usually indicates a long press operation).

var touchElement = document.getElementById('touch-element');

touchElement.addEventListener('touchstart', function(event) {
  console.log('Touch started');
});

touchElement.addEventListener('touchend', function(event) {
  console.log('Touch ended'); 
});

touchElement.addEventListener('touchmove', function(event) {
  if (event.touches.length == 1) {
    console.log('Long press detected');
  }
});

In this code, we use touchstart, touchend and touchmove events to detect the user's finger touch operation. When the user presses or releases their finger, the console will output "Touch started" and "Touch ended"; when the user performs a long press, the console will output "Long press detected".

It should be noted that there are relatively few methods of using Touch events to capture keyboard input information, and they are only suitable for some specific scenarios that require gesture input.

Summary

As we have seen, there are many ways to obtain keyboard input information on mobile devices. We can use keyboard events, input events, and Touch events to complete corresponding operations.

However, it should be noted that the method of obtaining keyboard input information on mobile devices is more complicated than on desktop. Keyboard events and Touch events may behave differently on different mobile devices and browser environments. Therefore, when implementing the keyboard input function on mobile devices, sufficient testing and debugging work needs to be done to ensure the compatibility, reliability, and usability of the code.

In addition, in the process of implementing the keyboard input function, we also need to consider security issues. Because JavaScript scripts can be accessed and modified at will, user-entered information needs to be handled carefully to prevent data from being tampered with and stolen. The best practice is to validate and filter user input on the server side to improve the security and reliability of your website and applications.

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