BigInt & Number Precision

BigInt is a numeric type for integers of arbitrary size — written with an n suffix like 10n — that stays exact beyond Number.MAX_SAFE_INTEGER , where ordinary floating-point numbers start to round.

Learn BigInt & Number Precision in our free JavaScript course — an interactive lesson with runnable examples, a practice exercise and a quick reference.

Part of the free JavaScript course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

It is the right tool for huge IDs, precise counters, and big sums where losing a single digit would be a real bug.

📚 Prerequisites: You should know JavaScript numbers and basic arithmetic . BigInt is a second numeric type that sits alongside the regular number .

🔢 Real-World Analogy: A regular number is a calculator with a fixed screen width :

JavaScript numbers are 64-bit doubles. They store integers exactly only up to Number.MAX_SAFE_INTEGER (9,007,199,254,740,991). Above that, consecutive integers start to collide — x + 1 can equal x . That's why a 19-digit database ID stored as a plain number can silently corrupt.

Check safety: Number.isSafeInteger(x) tells you whether an integer can be represented exactly as a regular number.

Make a BigInt by appending n to an integer literal, or by calling BigInt(value) on a number or numeric string. Arithmetic works as usual — + , - , * , ** — and stays exact no matter how large. Its typeof is "bigint" .

Integer division truncates: there are no fractions in BigInt, so 7n / 2n is 3n , not 3.5 . The remainder is available via % .

You cannot mix BigInt and Number in the same arithmetic — 10n + 5 throws a TypeError. Convert one side first: 10n + BigInt(5) or Number(10n) + 5 . Loose equality ( == ) compares across types, but strict equality ( === ) also checks the type. And JSON.stringify throws on a BigInt unless you convert it (often to a string) yourself.

Use BigInt for IDs and counters where exactness matters. For money, prefer integer cents in a regular number, or a decimal library — BigInt has no fractions.

Add two BigInt values exactly. Remember both operands must be BigInt.

Predict the output before revealing the answer.

bigint — the n suffix makes a BigInt, a distinct primitive type.

2n — BigInt division truncates toward zero; there are no decimals.

false — strict equality also compares the type, and bigint !== number.

Add a list of very large integers exactly using BigInt and reduce.

Up next: Checkpoint: Modern JavaScript — put it all together. 🏁

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