Help on simple JavaScript challenge

Here is my code, why won't it work for this challenge? How would you do this challenge? Thanks.

https://codepen.io/DragonG/pen/VJYzox

In this little assignment you are given a string of space separated numbers, and have to return the highest and lowest number.

Example:

highAndLow("1 2 3 4 5"); // return "5 1" highAndLow("1 2 -3 4 5"); // return "5 -3" highAndLow("1 9 3 4 -5"); // return "9 -5" 
submitted by /u/LovelyLionLily
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