There are many areas where we need random data.
One of them is testing. We may need random data: text, numbers etc, to test things out well.
Math.random(). But if something goes wrong, we’d like to be able to repeat the test, using exactly the same data.
For that, so called “seeded pseudo-random generators” are used. They take a “seed”, the first value, and then generate next ones using a formula. So that the same seed yields the same sequence, and hence the whole flow is easily reproducible. We only need to remember the seed to repeat it.
An example of such formula, that generates somewhat uniformly distributed values:
next = previous * 16807 % 2147483647
If we use
1 as the seed, the values will be:
- …and so on…
The task is to create a generator function
pseudoRandom(seed) that takes
seed and creates the generator with this formula.
let generator = pseudoRandom(1); alert(generator.next().value); // 16807 alert(generator.next().value); // 282475249 alert(generator.next().value); // 1622650073
Please note, the same can be done with a regular function, like this:
That also works. But then we loose ability to iterate with
for..of and to use generator composition, that may be useful elsewhere.