simple generators example

example-generators.js

// Demo: https://repl.it/@RandieBemis/ExampleES6Generators

// This is our generator function
// Each time it yields, it returns control to the caller of
// its iterators next() method
// A generator is a function that returns an iterator.
// An iterator is an object with a next() method.
function* g() {
  yield 1;
  yield 2;
  yield 3;
  yield 4;
}


console.log("\n// Part 1");
const gIterator = g(); // returns g's iterator
console.log(gIterator.next().value); // 1
console.log(gIterator.next().value); // 2
console.log(gIterator.next().value); // 3
console.log(gIterator.next().value); // 4
console.log(gIterator.next().done);  // true => We're done!


// for..of is a more convenient way to step thru all of g()'s values.
// g() returns its iterator. for..of automatically calls next() on
// that iterator, saves the value returned, until done. Basically it
// does everything we did manually above.
console.log("\n// Part 2");
for (const value of g()) {
  console.log(`value = ${value}`);
}


// calling g() resets its iterator back to the first value
console.log("\n// Part 3");
console.log(g().next().value); // 1
console.log(g().next().value); // 1


console.log("\n// Part 4");
for (const [index, value] of [1,2,3,4].entries()) {
  console.log(index, value);
}


/*
// Output using Babel Compiler v6.4.4  

// Part 1
1
2
3
4
true

// Part 2
value = 1
value = 2
value = 3
value = 4

// Part 3
1
1

// Part 4
0 1
1 2
2 3
3 4
*/