JS BigInt

JavaScript BigInt: Arbitrary-Precision Integers

BigInt is a primitive numerical type introduced in ES2020 that can represent integers of arbitrary magnitude beyond Number.MAX_SAFE_INTEGER ($2^{53} - 1$).

BigInt vs Number Comparison

flowchart LR
    BigIntType["BigInt Primitive (Suffix 'n')"] --> Limit1["No Upper Safety Boundary"]
    NumberType["Number Primitive (64-Bit Float)"] --> Limit2["Safe up to 9,007,199,254,740,991"]

Key Differences

Practical Code Example

// Demonstrating BigInt creation, arithmetic, and mixing restrictions

// 1. Creating BigInt Values
const hugeInt1 = 9007199254740995n; // Append 'n' suffix
const hugeInt2 = BigInt("900719925474099999999999999");

console.log(`BigInt 1: ${hugeInt1}`);
console.log(`Typeof hugeInt1: ${typeof hugeInt1}`); // "bigint"

// 2. BigInt Arithmetic
const sum = hugeInt1 + 10n;
const product = hugeInt1 * 2n;
console.log(`BigInt Sum: ${sum}`);
console.log(`BigInt Product: ${product}`);

// 3. Division Truncation (No decimals)
const divResult = 7n / 2n;
console.log(`BigInt 7n / 2n: ${divResult}`); // 3n (Fractional part dropped!)

// 4. Mixing Restriction Pitfall & Solution
const standardNum = 100;
// const invalidSum = hugeInt1 + standardNum; // Throws TypeError: Cannot mix BigInt and other types

const validSum = hugeInt1 + BigInt(standardNum); // Explicit conversion required
console.log(`Safely mixed sum: ${validSum}`);

Best Practices & Gotchas

• Do Not Use BigInt for Currency without Cent Conversion: Because BigInt truncates division fractional parts, scale values to cents or smallest currency units before dividing.
• JSON Serialization Pitfall: JSON.stringify() throws a TypeError on objects containing BigInt unless a custom replacer function or toJSON prototype method is provided.
• Strict Equality (===): 42n === 42 returns false because they are different primitive types. Loose equality 42n == 42 returns true.

Self-Check Challenge

Write a function serializeBigInt(key, value) for JSON.stringify() that converts BigInt values to string representation with an "n" suffix.