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JavaScript recursive generators are a powerful tool that can be used to implement recursive algorithms in a more memory-efficient way. In this article, we'll explore what recursive generators are, how they work, and how developers can use them in their own projects.

**What are JavaScript Recursive Generators?**

In JavaScript, a generator is a special type of function that can be used to create an iterator. Generators are defined using the `function*`

syntax and can be paused and resumed at any time using the `yield`

keyword.

Recursive generators are a variant of generators that allow a generator function to call itself recursively. This can be useful for implementing recursive algorithms, such as tree traversals or recursive descent parsers.

Here is an example of a recursive generator that generates the Fibonacci sequence

```
function* fibonacci(n) {
let a = 0,
b = 1;
for (let i = 0; i < n; i++) {
yield a;
[a, b] = [b, a + b];
}
}
for (let i of fibonacci(10)) {
console.log(i);
}
```

Output

```
0
1
1
2
3
5
8
13
21
34
```

In this example, the generator function called `fibonacci`

that takes in a number `n`

as an argument. The function uses a for loop to iterate `n`

times. Then, itt initializes two variables `a`

and `b`

to 0 and 1 respectively. On each iteration of the loop, the function yields the current value of `a`

and then updates the value of `a`

and `b`

using destructuring assignment, to be the current value of `b`

and the sum of `a`

and `b`

respectively.

**How Recursive Generators Work**

Recursive generators work by creating a new generator instance each time the generator function is called recursively. These generator instances are stored on the call stack, allowing the generator function to pause and resume execution as needed.

Here is a simplified version of the generator functions that illustrates how recursive generators work:

```
function* generate(n) {
if (n > 1) {
let gen = generate(n - 1);
yield* gen;
}
yield n;
}
for (let i of generate(10)) {
console.log(i);
}
```

Output

```
1
2
3
4
5
6
7
8
9
10
```

In this example, the `generate`

generator function takes a single argument ** n** and calls itself recursively if

**is greater than**

`n`

**. Each recursive call creates a new generator instance, which is stored on the call stack.**

`1`

The generator function then uses the `yield*`

operator to delegate to the inner generator. This causes the inner generator to execute until it reaches a `yield`

statement, at which point control is returned to the outer generator.

This process continues until the innermost generator reaches the end of its execution, at which point control is returned to the outer generator and the call stack is unwound.

**How Developers Can Use Recursive Generators**

Recursive generators can be a useful tool for developers who need to implement recursive algorithms in JavaScript. They allow developers to write recursive algorithms in a more memory-efficient way, as the generator instances are stored on the call stack rather than in the heap.

Developers can use recursive generators in a variety of contexts, including tree traversals, recursive descent parsers, and other applications that involve recursive data structures.

Recursive generators can also be useful for implementing lazy algorithms, where the result of an operation is not computed until it is needed. This can be useful for optimizing the performance of certain types of algorithms, such as search algorithms that may not need to compute the entire result in order to find the desired result.

For example, here is a recursive generator that implements a lazy search algorithm

```
function* search(items, predicate) {
for (let item of items) {
if (predicate(item)) {
yield item;
} else if (Array.isArray(item)) {
yield* search(item, predicate);
}
}
}
let results = search([1, [2, 3], [4, [5, 6]]], (x) => x % 2 === 0);
console.log(results.next().value);
```

Output

```
2
```

In this example, the ** search** generator function takes an array of items and a predicate function as arguments. It iterates over the items and yields the first item that satisfies the predicate. If the item is an array, the generator function calls itself recursively to search the array.

**Summary**

In summary, recursive generators are a powerful tool for implementing recursive algorithms in JavaScript. They allow developers to write recursive algorithms in a more memory-efficient way, and can be useful for a variety of applications, including tree traversals and lazy algorithms. Developers can use recursive generators to optimize the performance of their code and make it easier to work with recursive data structures.

## References

Iterators and generators - JavaScript | MDN (mozilla.org)

Recursive Generators in JavaScript - Stack Overflow