JavaScript Integer Safety

Written by Swapnil RajaPublished 24 Aug 2026

JavaScript numbers are only exact up to a certain size, after which BigInt takes over.

The limit is about nine quadrillion.

Beyond it, whole numbers stop being reliable.

Example

javascript

console.log(Number.MAX_SAFE_INTEGER);
console.log(Number.MAX_SAFE_INTEGER + 1 === Number.MAX_SAFE_INTEGER + 2);

The second line is true, which should be impossible.

Past the safe limit, different numbers can compare as equal.

Safe Integers

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Example

javascript

const big = 10n;
let message;

try {
  const result = big + 5;
} catch (error) {
  message = "cannot mix BigInt and Number";
}

console.log(message);
console.log(big + BigInt(5));

Complete Example

html

<!DOCTYPE html>
<html>
<head>
  <title>JavaScript Integer Safety</title>
</head>
<body>

  <h1>Integer Safety</h1>

  <p id="out"></p>

  <script>
    const limit = Number.MAX_SAFE_INTEGER;

    document.getElementById("out").innerHTML =
      "Largest safe integer: " + limit +
      "<br>Beyond it, +1 equals +2: " + (limit + 1 === limit + 2) +
      "<br>With BigInt: " + (BigInt(limit) + 1n === BigInt(limit) + 2n) +
      "<br>Is 42.5 an integer: " + Number.isInteger(42.5);
  </script>

</body>
</html>

JavaScript Integer Safety

Example

Safe Integers

Syntax

Checking for a Whole Number

Example

Safe Versus Unsafe

Example

BigInt for Large Values

Example

BigInt Does Not Mix

Example

When It Matters

Example

Complete Example

Try It Yourself

Important Points

Conclusion