SOURCE

/**
 * 默认情况下Number只能表示-(2^53-1)到2^53
 */
let plainNum = 9007199254740992; // 2^53
console.log(plainNum+3); // 失去精度了
console.log(typeof plainNum);

let bigNum = 9007199254740992n; // 2^53  bigInt(9007199254740992n)
console.log(bigNum+3n); // 精确计算

console.log(typeof bigNum);