Why does setting an input box with width 0 on Android and iOS lead to a difference in input direction?

Analysis of the difference in input direction of input box with width 0 under Android and iOS systems

A common problem when developing OTP input components is: in Android and iOS systems, when the input box width is set to 0, the input direction will be different. The iOS system performs normally, while the Android system has abnormal input from right to left. This article will explore in-depth the reasons for this difference.

In the question code snippet, after clicking the "Start Input" button, the input under iOS system is normal, but the input direction under Android system is reversed from right to left. style="width: 0;" This line of code is the key to the problem. After setting the width to a non-zero value, the input direction of the Android system can return to normal.

<meta charset="utf-8">
<meta content="width=device-width, initial-scale=1" name="viewport">
<title></title>
<button id="test_button">Start typing</button>
<div>Current input content:<span id="test_span"></span>
</div>
<input id="test_input" type="text" style="width: 0;">

<script>
  document.getElementById('test_button').addEventListener('click', () => {
    document.getElementById('test_input').focus();
  });

  setInterval(() => {
    document.getElementById('test_span').innerText = document.getElementById('test_input').value;
  }, 0);
</script>

This difference is not a code error, but is caused by different processing mechanisms of input boxes with width 0 by Android and iOS systems:

1. Android system mechanism: The Android system treats input boxes with width 0 as invisible elements, but still allows input. However, due to its zero-width nature, the Android system may default its input direction to from right to left, which may be compatible with input habits in some languages.

2. iOS system mechanism: iOS system treats the input box with width 0 as a visible input area and maintains the default input direction from left to right. This reflects the different design concepts of iOS and Android when dealing with such special situations.

To ensure cross-platform consistency, it is recommended to set the input box width to a non-zero value, or adjust the display method of the input box through CSS to avoid input direction problems caused by system differences. This is not a bug, but a difference in designs between different operating systems.

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