如何在原生JavaScript中为TextEncoder指定所需字符编码？或获取指定编码的字符码？

You’re right to call out that TextEncoder only supports UTF-8—any encoding parameter you pass gets ignored (it’s not part of the standard API). The good news is we can use TextDecoder (which does support encodings like ibm866) in a clever way to get the byte value for a given character without relying on pre-built arrays or external services.

Solution: Sync Function Using TextDecoder #

Since CP866 is a single-byte encoding (each character maps to exactly one byte between 0-255), we can iterate through all possible byte values and check which one decodes to your target character:

function getByteForCharInEncoding(char, encoding) {
  const decoder = new TextDecoder(encoding);
  // Iterate through all possible byte values (0-255)
  for (let byteValue = 0; byteValue < 256; byteValue++) {
    const byteBuffer = new Uint8Array([byteValue]);
    if (decoder.decode(byteBuffer) === char) {
      return byteValue;
    }
  }
  // Return null if the character isn't present in the encoding
  return null;
}

// Example usage for 'А' in CP866
console.log(getByteForCharInEncoding('А', 'ibm866')); // Output: 192

How This Works #

1. We create a TextDecoder instance configured for ibm866.
2. We loop through every possible byte value (0 to 255, since CP866 uses single bytes).
3. For each byte, we decode it to a character using the decoder.
4. When we find the byte that decodes to our target character, we return its value.

This is pure native JavaScript, no external dependencies or pre-defined arrays required. It works for any single-byte encoding supported by your browser’s TextDecoder implementation (most modern browsers support ibm866 out of the box).

Notes #

• If you need to encode entire strings instead of single characters, you could extend this function to process each character in the string and collect the corresponding bytes.
• For multi-byte encodings, this approach won’t work, but since CP866 is single-byte, it’s a perfect fit.

内容的提问来源于stack exchange，提问作者repulsor