Explain Generator function in ES6?

Generators are functions that can be exited and later re-entered. Their context (variable bindings) will be saved across re-entrances. A function keyword followed by an asterisk defines a generator function, which returns a Generator object.

Generator Function Example.

function* generator(i) {
  yield i;
  yield i + 10;
}

var gen = generator(10);

console.log(gen.next().value);
// expected output: 10

console.log(gen.next().value);

Further reading: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/function*