Not ES2020

[weaweawe01]

espree.tokenize("alert(1n)")
Uncaught [SyntaxError: Identifier directly after number
] {
index: 7,
lineNumber: 1,
column: 8
}

[aladdin-add]

bigint is supported, you need to pass the ecmaVersion >= 2020 or "latest".

espree.tokenize("1n", {ecmaVersion: 2020});