JavaScript Exponentiation Assignment

LeftHandSideExpression **= AssignmentExpression

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Type Coercion and Evaluation

• If the operands are strings, booleans, or objects, they are implicitly coerced into numeric types (Number or BigInt). For example, an object whose valueOf() method returns a BigInt will be coerced into a BigInt, whereas a string like "5" will be coerced into a Number.
• The operator supports both Number and BigInt primitives.
• The resulting assigned value will match the type of the operands after they have been coerced to numeric types, not their original evaluated type.

// Standard Number evaluation
let base = 3;
base **= 4; 
console.log(base); // 81

// BigInt evaluation
let bigBase = 2n;
bigBase **= 3n; 
console.log(bigBase); // 8n

// Implicit Type Coercion
let strBase = "5";
strBase **= 2; // String "5" is coerced to Number 5
console.log(strBase); // 25
console.log(typeof strBase); // "number" (matches the coerced type, not the original String)

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Associativity

let a = 2;
let b = 3;
a **= b **= 2; 

// Evaluates as: a **= (b **= 2)
// b becomes 9
// a becomes 2 ** 9
console.log(a); // 512
console.log(b); // 9

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Exceptions and Edge Cases

• Type Mixing: Attempting to mix BigInt and Number operands without explicit conversion will throw a TypeError.
• Negative Bases with Fractional Exponents: If the base is a negative number and the exponent is a fraction, the operation yields NaN because JavaScript does not support imaginary numbers in standard numeric types.

let mixedBase = 5n;
// mixedBase **= 2; // Throws TypeError: Cannot mix BigInt and other types

let negBase = -4;
negBase **= 0.5; // Equivalent to the square root of -4
console.log(negBase); // NaN