What does console.log(0.1 + 0.2) output?

Console output

Why

JavaScript numbers are IEEE 754 double-precision floats stored in base 2. Just as 1/3 cannot be written exactly in base 10, 0.1 and 0.2 cannot be represented exactly in base 2, so their sum carries a tiny rounding error. The result is the nearest representable double, 0.30000000000000004.