The Number.isSafeInteger() method determines whether the provided value is a number that is a safe integer.

A safe integer is an integer that

  • can be exactly represented as an IEEE-754 double precision number, and
  • whose IEEE-754 representation cannot be the result of rounding any other integer to fit the IEEE-754 representation.

For example, 253 - 1 is a safe integer: it can be exactly represented, and no other integer rounds to it under any IEEE-754 rounding mode. In contrast, 253 is not a safe integer: it can be exactly represented in IEEE-754, but the integer 253 + 1 can't be directly represented in IEEE-754 but instead rounds to 253 under round-to-nearest and round-to-zero rounding. The safe integers consist of all integers from -(253 - 1) inclusive to 253 - 1 inclusive (± 9007199254740991 or ± 9,007,199,254,740,991).

Handling values larger or smaller than ~9 quadrillion with full precision requires using an arbitrary precision arithmetic library. See What Every Programmer Needs to Know about Floating Point Arithmetic for more information on floating point representations of numbers.

For larger integers, consider using the BigInt type.




The value to be tested for being a safe integer.

Return value

A Boolean indicating whether or not the given value is a number that is a safe integer.


Number.isSafeInteger = Number.isSafeInteger || function (value) {
   return Number.isInteger(value) && Math.abs(value) <= Number.MAX_SAFE_INTEGER;


Using isSafeInteger

Number.isSafeInteger(3);                    // true
Number.isSafeInteger(Math.pow(2, 53));      // false
Number.isSafeInteger(Math.pow(2, 53) - 1);  // true
Number.isSafeInteger(NaN);                  // false
Number.isSafeInteger(Infinity);             // false
Number.isSafeInteger('3');                  // false
Number.isSafeInteger(3.1);                  // false
Number.isSafeInteger(3.0);                  // true


Browser compatibilityUpdate compatibility data on GitHub

Chrome Edge Firefox Internet Explorer Opera Safari
isSafeInteger 34 12 32 No 21 10
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
isSafeInteger ≤37 34 32 21 10 2.0
isSafeInteger 0.12

See also

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