Javascript - Replace substring if the substring is not prepended with a character Regex or other

Question

I need to replace all instances of a string(needle) within another string(haystack), but only where the needle is not preceeded by a specific character, in this case '-'

var needle = 'secret';
var haystack = 'secret title date user -secret secret something.secret';

//Regex that needs to be adjusted
var result = haystack.replace(/secret/g, '');

//Desired result is
var desiredResult = ' title date user -secret  something.';