Experience with Javascript

gistfile1.txt

We first started out with CSS and Html.  I learned the rules of both but I think I didn't have a concise method of doing either so
I was just slapping code together and seeing if it would work.  This last weekend when I worked on my portfolio, I noticed that I was
taking a more measured approached to both of these languages.  I feel more confident about them now.  As far as Javascript is 
concerned, I felt more comfortable because it is more of a procedural language which I am more comfortable with.  React has 
a big learning curve and I feel I am starting to make real improvements in it.  My goal is to write React code with very little help.

https://www.codewars.com/users/krock/completed_solutions

function invert(array) {
  if (array.length === 0){
    return array
  }
   z = array.map(function (a) {
    if (a === 0) {
      return 0     
    } else {
      return -a
    }
  })
     return z  
}


function stringClean(s) {
z = []
z = s.split("")

z = z.map( (a) => { 
if ((parseInt(a)) || (parseInt(a) === 0)){ 
  return ''
} else if (a === ','){
  return 'comma'
} else { 
  return  a 
} }) 

let a = z.toString().replace(/,/g, '')
return a.toString().replace(/comma/g, ',')
}