Log all Prime Numbers until `n` using Javascript Generators
I was interviewing with few companies a couple of months back for a Frontend/Fullstack position. One of the most interesting questions I faced in one of the coding exams was to Write a function in JavaScript that takes an input `n` and return all the prime numbers until `n`. The question is simple and straight forward as you see it.
I quickly wrote the following code and it worked perfectly!
BOOM! I’m done. I felt happy and ran the test cases. Of course, they failed. Happiness is a myth in Javascript. There was a trick here and this was the provided main method that calls my function…
function main() {
const primeNumberGenerator = getAllPrimeNumbers(23);
let primeNumber;
while ((primeNumber = primeNumberGenerator.next().value) !== undefined) {
console.log(primeNumber);
}
}I observed some new keywords like next(), I remember to have seen something similar to this in RxJS but this was a pure Javascript code so this should mean something different. I googled and found something new in Javascript that I have rarely used/heard before - Generators in Javascript. It was a timed test, so I quickly read through articles, examples and fixed my code.
It worked and all tests passed!
Generators can return (“yield”) multiple values, one after another, on-demand. They work great with iterables, allowing to create data streams with ease.
I don’t want to talk more about generators as there are better articles that do this. I have attached a few at the end that helped me in this course of learning.
This was one of the most interesting things I got to solve as part of the interviews. I wrote code to solve a simple problem but with lazy evaluation and memory efficiency. This was fun.
Few Articles that helped me to quickly understand Generators and Iterators -
- https://javascript.info/generators
- https://codeburst.io/understanding-generators-in-es6-javascript-with-examples-6728834016d5
I hope this was helpful to you to explore how we can use generators in our everyday code.
