Exponentiation assignment (**=)

The exponentiation assignment operator (**=) raises the value of a variable to the power of the right operand.

Operator: x **= y
Meaning:  x  = x ** y

// Assuming the following variable
//  bar = 5

bar **= 2     // 25
bar **= 'foo' // NaN

• Assignment operators in the JS guide
• Exponentiation operator