Understanding fat arrows

Without fat arrows.js

//https://greenin.space/how-do-you-write-an-asynchronous-for-loop-in-javascript/

var N = 5

function asyncFunc (cb) {  
  console.log("in asyncFunc")
  setTimeout(cb(Math.random()), 3000)
  console.log("out asyncFunc")
}

function loop (max, results, done) {  
  // Recursion base-case
  if (results.length >= max) return done(results)
console.log("in loop")
  asyncFunc((res) => {
    results.push(res)
    loop(max, results, done)
  })
}

var randomNumbers = []  
loop(N, randomNumbers, function (results) {  
  console.log(results)
})

/*
BAM! Everything output at once! NO TIMEOUT PAUSES AT ALL

VM224:13 in loop
VM224:5 in asyncFunc
VM224:13 in loop
VM224:5 in asyncFunc
VM224:13 in loop
VM224:5 in asyncFunc
VM224:13 in loop
VM224:5 in asyncFunc
VM224:13 in loop
VM224:5 in asyncFunc
VM224:22 [0.6260232019703835, 0.3711804535705596, 0.36812554858624935, 0.2748239105567336, 0.9398391374852508]
VM224:7 out asyncFunc
VM224:7 out asyncFunc
VM224:7 out asyncFunc
VM224:7 out asyncFunc
VM224:7 out asyncFunc
*/