Why Is My PHP AJAX Response Text Failing String Comparisons?

Avoiding Character 65279 Echoing in PHP

When receiving a response via AJAX callback, you may encounter an issue where the retrieved text (xmlhttp.responseText) appears correct, but comparisons against a specific string yield false results. This is often caused by the presence of an invisible character with a charCodeAt(0) of 65279.

Understanding Character 65279

Character 65279 is a Unicode Control Character (Unicode codepoint U FEFF) that specifies the endianness of the Unicode encoding:

• Big-Endian: Bytes are stored in the order most significant byte first.
• Little-Endian: Bytes are stored in the order least significant byte first.

Causes of Character 65279 Echoing

Character 65279 is typically added to UTF-8 encoded files by editors like Windows Notepad. When a PHP file is included into another, it can introduce this character, resulting in unexpected behavior.

Solution

To avoid character 65279 echoing, you can:

• Use a Text Editor Without BOM: Edit the PHP files using editors like Notepad that allow saving in UTF-8 encoding without a Byte Order Mark (BOM).
• Save PHP Files with ANSI Encoding: Save the PHP files that do not use extended characters in ANSI encoding.
• Remove Character 65279 Manually: Check the beginning of the responseText and if it contains character 65279, remove it before comparing.

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