The JavaScript exception "can't convert BigInt to number" occurs when an arithmetic operation involves a mix of BigInt and Number values.
Message
TypeError: Cannot mix BigInt and other types, use explicit conversions (V8-based)
TypeError: BigInts have no unsigned right shift, use >> instead (V8-based)
TypeError: can't convert BigInt to number (Firefox)
TypeError: Invalid mix of BigInt and other type in addition/multiplication/…. (Safari)
TypeError: BigInt does not support >>> operator (Safari)
Error type
What went wrong?
The two sides of an arithmetic operator must both be BigInts or both not. If an operation involves a mix of BigInts and numbers, it's ambiguous whether the result should be a BigInt or number, since there may be loss of precision in both cases.
The error can also happen if the unsigned right shift operator (>>>) is used between two BigInts. In Firefox, the message is the same: "can't convert BigInt to number".
Examples
Mixing numbers and BigInts in operations
const sum = 1n + 1;
// TypeError: can't convert BigInt to number
Instead, explicitly coerce one side to a BigInt or number.
const sum = 1n + BigInt(1);
const sum2 = Number(1n) + 1;
Using unsigned right shift on BigInts
const a = 4n >>> 2n;
// TypeError: can't convert BigInt to number
Use normal right shift instead.
const a = 4n >> 2n;