fibonacciUsingGenerator.js

function* makeFibonacciSequenceGenerator(endIndex = Infinity) {
    let previousNumber = 0;
    let currentNumber = 1;
    
    for (let currentIndex = 0; currentIndex < endIndex; currentIndex++) {
        yield currentNumber;
        let nextNumber = currentNumber + previousNumber;
        previousNumber = currentNumber;
        currentNumber = nextNumber;
    }
}

let fibonacciSequenceGenerator = makeFibonacciSequenceGenerator(5);

for (let x of fibonacciSequenceGenerator) {
    console.log(x);
}