You can learn more about iterators and generators here:

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Iterators_and_Generators
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/function*
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/GeneratorFunction
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Generator
• https://davidwalsh.name/es6-generators
• https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-3.html