Obfuscated JavaScript

Given enough time, any language will evolve into Perl.

($=(_,__=0)=>_?$(_.slice(1),+_[0]?__+(2**(_.length-1)):__):__)("10");
// --> 2

function binstr2dec(binstr, num=0) {
  if(binstr.length) {
    if(parseInt(binstr.substring(0, 1), 10)) {
      num += Math.pow(2, binstr.length - 1);
    }
    const rest = binstr.substring(1);
    return binstr2dec(rest, num);
  } else {
    return num;
  }
}

---

(_=$=>$<=0?1:$*_($-1))(5);
// --> 120

function factorial(n) {
  if(n <= 0) {
    return 1;
  }
  return n * factorial(n - 1);
}

---

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