Regression: defaultValue for <textarea> broken in IE11 (PR #2742)

[ivanq2191-ui]

Describe the bug
In Preact 10.5.0 and later, the defaultValue prop for <textarea> no longer works in Internet Explorer 11 when the value prop is not explicitly passed. The textarea appears empty despite having a defaultValue set. This worked correctly in earlier versions.

To Reproduce
Steps to reproduce the behavior:

1. Create a Preact component with <textarea defaultValue="Hello, World!" />
2. Open the application in Internet Explorer 11
3. Observe that the textarea is empty
4. Add value={undefined} to the component: <textarea defaultValue="Hello, World!" value={undefined} />
5. Observe that the textarea now displays the text

Expected behavior
The textarea should display the value passed to defaultValue in all browsers, including Internet Explorer 11, without requiring value={undefined} to be explicitly passed.

Regression Commit: This issue was introduced in PR #2742 - [wip] optimizations for compat.

Before (working):

// Old condition: checks if valueProp is null (meaning value hasn't been set yet)
if (i === 'defaultValue' && valueProp == null) {
    if ('value' in props) {
        i = 'value';
    } else {
        valueProp = value; // Preserve defaultValue as fallback
    }
}

// New condition: only works if value prop exists AND is null/undefined
if (i === 'defaultValue' && 'value' in props && props.value == null) {
    i = 'value';
}

The Problem:

The old logic handled two cases:

• value is present (even null) → use it
• value is absent → use defaultValue as fallback (valueProp = value)

The new logic handles only one case:

• value={null} or value={undefined} is explicitly passed → transform to value
• value is absent → defaultValue is silently ignored

Why This Is a Regression:
The new condition 'value' in props && props.value == null is fundamentally different from valueProp == null.
By removing the else branch, the refactoring lost the ability to handle the case where value is simply not provided. This was a critical fallback for IE11 compatibility.