CODEWITHSUNDEEP
javascriptecmascript-6iteratorgenerator
John Abraham
John Abraham

Reputation: 18781

How to convert simple iterator to javascript generator

CODEPEN

Trying to wrap my head around generator and I just don't get it.

I have a simple non generator iterator class called KeyGen that I would like to rewrite using JS generators:

If this isn't what generators are suppose to do than please leave a comment and I'll close

class KeyGen {
  constructor(numOfKeys) {
    this.keys = new Array(numOfKeys).fill(0).map((i, index) => index);
    this.iteratorCount = 0;
  }

  keyIterator() {
    return {
      next: () => this.keys[this.iteratorCount++]
    }
  }
}

const keyGen = new KeyGen(4);

console.log(keyGen.keyIterator().next());
console.log(keyGen.keyIterator().next());
console.log(keyGen.keyIterator().next());
console.log(keyGen.keyIterator().next());

Upvotes: 2

Views: 478

Answers (2)

CRice
CRice

Reputation: 32146

A generator would be a good fit here, but you should note that your original code is not the same as generator. For a generator, the next call should return an object with two keys, value and done.

To convert to a generator function, you just need to build the initial list to iterate over in the same way you do now, but then you can just use a normal for loop to yield each element one by one.

Example:

function* KeyGen(numOfKeys) {
    const keys = Array(numOfKeys)
      .fill(0)
      .map((i, index) => index);
      
    for (let key of keys) {
      yield key;
    }
}

const keyGen = KeyGen(4);

console.log(keyGen.next())
console.log(keyGen.next())
console.log(keyGen.next())
console.log(keyGen.next())
console.log(keyGen.next())

// For extra coolness, note that for/of loops are designed to work with generators:
for (let key of KeyGen(4)) {
    console.log(key)
}

Upvotes: 1

CertainPerformance
CertainPerformance

Reputation: 370679

It's pretty straightforward, just declare the array and then yield each element:

function* gen(length) {
  const keys = Array.from({ length }, (_, i) => i);
  for (const key of keys) yield key;
}

const iter = gen(3);
console.log(iter.next().value);
console.log(iter.next().value);
console.log(iter.next().value);

Upvotes: 2

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