Explain this javascript function to me

Brant Snow
Brant Snow used Ask the Experts™
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?
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Distinguished Expert 2017
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
Most Valuable Expert 2017
Distinguished Expert 2018
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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