Function to trim UTF-8 string to a given number of bytes

trim-utf8-string-to-bytes.js

const { StringDecoder } = require('string_decoder'),
      input = 'abc😧🤕',
      length = Buffer.byteLength(input);

function trimToSize(str, byteLength) {
   const decoder = new StringDecoder('utf8'),
         buffer = new Buffer(str);

   return decoder.write(buffer.slice(0, byteLength));
}

console.log('input:', input);
for (var i = 0; i <= length; i++) {
   const result = trimToSize(input, i);

   console.log(`${i}:\t${Buffer.byteLength(result)}\t[${Buffer.from(result).toString('hex')}]`, result);
}

🤦‍♂️ Fixed.