code: function NumberToFixedJS(fractionDigits) {
    var x = this;
    if (!IS_NUMBER(this)) {
      if (!IS_NUMBER_WRAPPER(this)) {
        throw MakeTypeError(kIncompatibleMethodReceiver,
                            "Number.prototype.toFixed", this);
      }
      // Get the value of this number in case it's an object.
      x = %_ValueOf(this);
    }
    var f = TO_INTEGER(fractionDigits);
  
    if (f < 0 || f > 20) {
      throw MakeRangeError(kNumberFormatRange, "toFixed() digits");
    }
  
    if (NUMBER_IS_NAN(x)) return "NaN";
    if (x == INFINITY) return "Infinity";
    if (x == -INFINITY) return "-Infinity";
  
    return %NumberToFixed(x, f);
  }
docs: ES6 20.1.3.3 Number.prototype.toFixed(fractionDigits)