The major currency biggest winner is the JPY
If you were to take the % changes of the major currencies vs. each other and added up those % changes, the winner for largest 2018 change was the JPY (it rose). The next biggest % changer was the AUD (the AUD fell).
The JPY rose vs. all the major currencies with gains against the AUD (AUDJPY) the largest at 12.2%. Versus the USD, the JPY only gained 2.6%. That was the smallest gain of the JPY vs. the majors. Today, the price of the USDJPY moved toward the midpoint of the years trading range at 109.572 (the low was in March at 104.60, while the high war reached in October at 114.544). The low today reached just above that midpoint level at 109.628.
With Japan GDP moving into the negative in the 3rd quarter, it can be a head-scratcher why the JPY is the strongest.
Typically, weaker economic growth is a precursor for a weaker currency. However, the Pavlovian reaction to lower stock prices is often a flight into the "relative safety of the JPY" and out of the "risk currencies" like the AUD, CAD and NZD.
Looking at the weakest currencies, the AUD led the way followed by the CAD. The NZD was mostly lower, but the GBP (and Brexit concerns) nosed it out.
As for the stock markets influence on currencies, 2018 was indeed full of lower global stock prices with the Shanghai Composite as major index with the largest decline at -24.59% from the end of 2017 year close. This too helps to explain the weakness in the AUD as the Australian economy is reliant on China's growth.
Overall, all the major indices are closing in the red this year (see chart below) which has helped to contribute to the JPYs rise and flow out of the risk currencies.
