TheCrypto.getRandomValues() method lets you get cryptographically strong random values.The array given as the parameter is filled with random numbers (random in its cryptographic meaning).

To guarantee enough performance, implementations are not using a truly random number generator, but they are using a pseudo-random number generatorseeded with a value with enough entropy.The pseudo-random number generator algorithm (PRNG) may vary acrossuser agents, but is suitable for cryptographic purposes.

getRandomValues() is the only member of theCrypto interface which can be used from an insecure context.

Syntax

getRandomValues(typedArray)

Parameters

typedArray

An integer-basedTypedArray, that is one of:Int8Array,Uint8Array,Uint8ClampedArray,Int16Array,Uint16Array,Int32Array,Uint32Array,BigInt64Array,BigUint64Array (butnotFloat16Array,Float32Array norFloat64Array).All elements in the array will be overwritten with random numbers.

Return value

The same array passed astypedArray but with its contents replaced with the newly generated random numbers.Note thattypedArray is modified in-place, and no copy is made.

Exceptions

QuotaExceededError

Thrown if thebyteLength oftypedArray exceeds 65,536.

Usage notes

Prefer thegenerateKey() method for key generation, which is guaranteed to be running in a secure context.

There is no minimum degree of entropy mandated by the Web Cryptography specification.User agents are instead urged to provide the best entropy they can when generating random numbers,using a well-defined, efficient pseudorandom number generator built into the user agent itself,but seeded with values taken from an external source of pseudorandom numbers, such as a platform-specific random number function,the Unix/dev/urandom device, or other source of random or pseudorandom data.

Examples

const array = new Uint32Array(10);self.crypto.getRandomValues(array);console.log("Your lucky numbers:");for (const num of array) {  console.log(num);}

Specifications

Browser compatibility

See also

• Web Crypto API
• Math.random, a non-cryptographic source of random numbers.