pseudorandom
Posted on Sunday, February 13, 2022 Suggest An EditI’m still tinkering around with the calendar maker. I decided to give each event (birthday, holiday, anniversary, etc.) a random id. Rather than just use Math.random(), I decided to try using the browser’s Crypto interface. There’s a nice function that generates a UUID (universally unique identifier): window.crypto.randomUUID(). The result looks something like this: 'a1d803ce-822e-4d2d-a68f-16f85a5c1508'. This is a 128 bit label which means there are 2128 unique values - around 3.4x1038 or roughly a trillion times a trillion times a trillion.
You can also generate random integers using getRandomValues, and following the format (replacing ARRAY): crypto.getRandomValues(new ARRAY(1))[0]. You can use any of the typed integer arrays in JavaScript.
| Array | Number of Values | Range |
|---|---|---|
| Int8Array | 28= 256 | [-128, 127] |
| Int16Array | 216= 65,536 | [-32768, 32767] |
| Int32Array | 232= 4,294,967,296 | [-2147483648, 2147483647] |
| Uint8Array | 28= 256 | [0, 255] |
| Uint16Array | 216= 65,536 | [0, 65535] |
| Uint32Array | 232= 4,294,967,296 | [0, 4294967295] |
| Uint8ClampedArray | 28= 256 | [0, 255] |
| BigInt64Array | 264 = 18,446,744,073,709,551,615 | [-9223372036854775808, 9223372036854775807] |
| BitUint64Array | 264 = 18,446,744,073,709,551,615 | [0, 18446744073709551615] |
The only difference between Uint8Array and Uint8ClampedArray is that the if you try assign a number outside of the range [0, 255], the clamped array will round you up to 0 or down to 255. The Uint8Array will take loop over, so 256 becomes 0, and -1 becomes 255, etc. I don’t think this has an effect on the random output code above though.
The “U” in the name stands for “unsigned”, meaning the numbers are non-negative. The signed versions have are just centered around zero, so there are an equal amount of negative and non-negative outcomes.