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Exponentiation assignment (**=)

The **exponentiation assignment (**=)** operator performs exponentiation on the two operands and assigns the result to the left operand.

x **= y

x **= y is equivalent to x = x ** y, except that the expression x is only evaluated once.

let bar = 5;

bar **= 2; // 25
bar **= "foo"; // NaN

let foo = 3n;
foo **= 2n; // 9n

Specification
ECMAScript Language Specification # sec-assignment-operators

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`Exponentiation_assignment`	52	14	52	39	10.1	52	52	41	10.3	6.0	51	1.0	7.0.0