I thought values entered in forms are properly encoded by browsers.
But this simple test file \"test_get_vs_encodeuri.html\" shows it\'s not true:
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This is a character encoding issue. Your document is using the charset Windows-1252 where the € is at position 128 that is encoded with Windows-1252 as 0x80. But encodeURICompenent is expecting the input to be UTF-8, thus using Unicode’s charset where the € is at position 8364 (PDF) that is encoded with UTF-8 0xE282AC.
A solution would be to use UTF-8 for your document as well. Or you write a mapping to convert UTF-8 encoded strings to Windows-1252.