code: function compress_block(ltree, dtree) {
  			var dist; // distance of matched string
  			var lc; // match length or unmatched char (if dist === 0)
  			var lx = 0; // running index in l_buf
  			var code; // the code to send
  			var extra; // number of extra bits to send
  
  			if (last_lit !== 0) {
  				do {
  					dist = ((that.pending_buf[d_buf + lx * 2] << 8) & 0xff00) | (that.pending_buf[d_buf + lx * 2 + 1] & 0xff);
  					lc = (that.pending_buf[l_buf + lx]) & 0xff;
  					lx++;
  
  					if (dist === 0) {
  						send_code(lc, ltree); // send a literal byte
  					} else {
  						// Here, lc is the match length - MIN_MATCH
  						code = Tree._length_code[lc];
  
  						send_code(code + LITERALS + 1, ltree); // send the length
  						// code
  						extra = Tree.extra_lbits[code];
  						if (extra !== 0) {
  							lc -= Tree.base_length[code];
  							send_bits(lc, extra); // send the extra length bits
  						}
  						dist--; // dist is now the match distance - 1
  						code = Tree.d_code(dist);
  
  						send_code(code, dtree); // send the distance code
  						extra = Tree.extra_dbits[code];
  						if (extra !== 0) {
  							dist -= Tree.base_dist[code];
  							send_bits(dist, extra); // send the extra distance bits
  						}
  					} // literal or match pair ?
  
  					// Check that the overlay between pending_buf and d_buf+l_buf is
  					// ok:
  				} while (lx < last_lit);
  			}
  
  			send_code(END_BLOCK, ltree);
  			last_eob_len = ltree[END_BLOCK * 2 + 1];
  		}
docs: Send the block data compressed using the given Huffman trees