Difference between ECMAScript 2016 exponentiation operator and Math.pow()

None. As you can read in the ES7 spec, both Math.pow and the ** exponentation operator cast their arguments/operands to numbers and use the very same algorithm to determine the result.

Addendum: this changed with the introduction of the BigInt type in ES2020, whose values are only supported by operators (including **) but not the Math object.

Late to the party -- I just wanted to add that as much as there is no difference between the two ways, I recently came to realize that the ** exponentiation operator isn't supported in Internet Explorer, so developers that are interested in extensive cross-browser support for their applications, may prefer to choose the Math.pow(...) over the exponentiation operator.