How to convert two 8bit number into 16bit in JavaScript

8bit_to_16bit.js

/*

  Problem: 
  
  You have 16 bit number, for example 12345. 
  In hexadecimal it looks like this: 0x3039, 
  but in the buffer it will look like this: <Buffer: 39 30>
  
  How to convert two 8 bit numbers back to 16 bit number?
  Bitwise operator '<<'

*/
  
  /* ----- Code ----- */
  let buffer = message.binaryData; // <Buffer: 39 30>
  let number = (buffer[1] << 8) + buffer[0]; // 12345

/*

  Explanation:
  
  Node buffer stores binary data in bytes (8 bit) in `Little Endian` order,
  in simple words your hex number will be reversed in order (0x3039 became [0x39, 0x30])
  To put two 8 bit numbers together we need bitwise operator '<<',
  which works similar to string concatenation ('abc' + '123' => 'abc123'),
  but because we're dealing with numbers we can't simply sum them up.
  So, we take second element it the buffer, shift it 8 bits to the left (30 => 30__)
  and add first element to it (30__ => 3039)
  
*/