# Generators

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```function* fibonacci(limit) { let [prev, curr] = [0, 1]; while (!limit || curr <= limit) { yield curr; [prev, curr] = [curr, prev + curr]; } } // bounded by upper limit 10 for (let n of fibonacci(10)) { console.log(n); } // generator without an upper bound limit for (let n of fibonacci()) { console.log(n); if (n > 10000) break; } // manually iterating let fibGen = fibonacci(); console.log(fibGen.next().value); // 1 console.log(fibGen.next().value); // 1 console.log(fibGen.next().value); // 2 console.log(fibGen.next().value); // 3 console.log(fibGen.next().value); // 5 console.log(fibGen.next().value); // 8 // picks up from where you stopped for (let n of fibGen) { console.log(n); if (n > 10000) break; }```
Example from Python, Cython:
`https://wiki.python.org/moin/Generators`
Example from C#:
```// Method that takes an iterable input (possibly an array) // and returns all even numbers. public static IEnumerable<int> GetEven(IEnumerable<int> numbers) { foreach (int i in numbers) { if ((i % 2) == 0) { yield return i; } } }```
Example from Ruby:
```# Generator from an Enumerator object chars = Enumerator.new(['A', 'B', 'C', 'Z']) 4.times { puts chars.next } # Generator from a block count = Enumerator.new do |yielder| i = 0 loop { yielder.yield i += 1 } end 100.times { puts count.next }```

Languages with Generators include JavaScript, Python, C#, Ruby, TypeScript, Cython, Static Typescript