Exponentiation (**)
  The exponentiation operator (**) returns the result of raising the first
  operand to the power of the second operand. It is equivalent to Math.pow,
  except it also accepts BigInts as operands.
Syntax
x ** y
Description
  The exponentiation operator is
  right-associative: a ** b ** c is equal to
  a ** (b ** c).
  In most languages, such as PHP, Python, and others that have an exponentiation operator
  (**), the exponentiation operator is defined to have a higher precedence
  than unary operators, such as unary + and unary -, but there
  are a few exceptions. For example, in Bash, the ** operator is defined to
  have a lower precedence than unary operators.
  In JavaScript, it is impossible to write an ambiguous exponentiation expression. That
  is, you cannot put a unary operator (+/-/~/!/delete/void/typeof)
  immediately before the base number; doing so will cause a SyntaxError.
-2 ** 2;
// 4 in Bash, -4 in other languages.
// This is invalid in JavaScript, as the operation is ambiguous.
-(2 ** 2);
// -4 in JavaScript and the author's intention is unambiguous.
Note that some programming languages use the caret symbol ^ for exponentiation, but JavaScript uses that symbol for the bitwise logical XOR operator.
Examples
Basic exponentiation
2 ** 3   // 8
3 ** 2   // 9
3 ** 2.5 // 15.588457268119896
10 ** -1 // 0.1
NaN ** 2 // NaN
Associativity
2 ** 3 ** 2   // 512
2 ** (3 ** 2) // 512
(2 ** 3) ** 2 // 64
Usage with unary operators
To invert the sign of the result of an exponentiation expression:
-(2 ** 2) // -4
To force the base of an exponentiation expression to be a negative number:
(-2) ** 2 // 4
Specifications
| Specification | 
|---|
| ECMAScript Language Specification # sec-exp-operator | 
Browser compatibility
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