Javascript - Collection Generator return

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Introduction

The iterators having two optional methods: return(...) and throw(...).

These methods end the sequence in a paused generator as soon as they are called. 

function *getFruits() { 
          yield "XML"; 
          yield "Keyboard"; 
          yield "Screen"; 
} 
const fruitIterator = getFruits(); 
console.log(fruitIterator.next());        // {value: 'XML', done: false} 
console.log(fruitIterator.return("kiwi"));// {value: 'kiwi', done: true} 
console.log(fruitIterator.next());        // {value: undefined, done: true}

Here, return("kiwi") returns the same value "kiwi" passed as the argument and ends the sequence resulting in done to be true.

This is equivalent to having a return value in the generator function.

Traversing the sequence obtained from a generator does not include the value that signals { done: true }.

The following code are iterating over the collection fruitIterator, which only contains the elements yielded before the return() method was invoked:

Demo

function *getFruits() { 
    yield "XML"; 
    yield "Keyboard"; 
    yield "Screen"; 
    return "kiwi"; 
    yield "watermelon"; 
} 

const fruitIterator = getFruits(); 

for (let fruit of fruitIterator) { 
    console.log(fruit); //from   w w  w .  ja  va 2 s . c o m
}

Result

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