How to get x of 2^x=8000? [duplicate]

Question

Possible Duplicate:
What's the opposite of JavaScript's Math.pow?

2^x=i

Given i, how can we calculate x using Javascript?

Answer 1

You want to take the logarithm of 8000. JS has the Math.log function which uses base e, you want base 2 so you can write Math.log(8000) / Math.log(2) to get the logarithm of 8000 base 2, which is equal to x.