Explain this javascript function to me

I was playing codewars, i came up with this
function nbDig(n, d) {
    // your code
    var count;
      var squared = (n*n).toString();
      var regex = new RegExp(d,"gi");
      var matches = squared.match(regex);
            count = count + matches.length;
    return count;

However one of the best practices submitted was the following below

function nbDig(n, d) {
var res=0;
    for (var g=0;g<=n;g++){
      var square=(g*g+"").split("");
    }return res;

I do not understand the (s)=>s==d

I believe that this is function(s){ s==d?res++:null}

Is that correct, can someone provide some good documentation or link for the (s)=> paradigm in javascript?
Brant SnowAsked:
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Leonidas DosasCommented:
From the begging:
(s)=>....... as function(=>) with argument (s) : similar   function (s)

s==d?  Conditional (ternary) Operator replace the... If (s==d)

res++  Increment res (res=res+1) //True condition

:null  Null if (s==d) false.


JavaScript Arrow Functions Introduction

Conditional (ternary) Operator
Julian HansenCommented:
Here is (in my opinion) the definitive link for JavaScript arrow functions

From this link
An arrow function expression has a shorter syntax than a function expression and does not bind its own this, arguments, super, or new.target. These function expressions are best suited for non-method functions, and they cannot be used as constructors.

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square is an array
the forEach operates on the array and passes each element to the function provided
The arrow function

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(s) - the current element in the array (square) being processed
The next bit is a ternary expression
(expr) ? if_true : if_false;

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Same as
if (s==d) {
  return res;
else {
   return null

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