Using Reduce to condense arrays

Tell us what’s happening:

I looked at the other posts made about this, but none were complete. I can’t get the correct output. I appear to use reduce right otherwise, just not correct in the math and I can’t see how! Thanks in advance!

Your code so far

var array = [4,5,6,7,8];
var singleVal = 0;

// Only change code below this line.

singleVal = array.reduce(function(previousVal,currentVal){
  return currentVal - previousVal;
}, 0);

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Link to the challenge:

“sum” means that the values of the array should all be added. You are subtracting them.