How to use math.pow when the base is a negative number and the exponent is a decimal?

Math.pow(-3, 2,6)would give me NaN

Would it be correct to turn it in the following:

if exponent number before the decimal point is even (turn negative into positive)): Math.pow(3, 2,6)

if exponent number before the decimal point is odd (turn negative into positive first and make result negative again after calculation):

Math.pow(3, 2,6)
= 157.49069663608591
// make negative: -157.49069663608591

Is this way plain wrong or is there another way without rounding up or down the exponent?