es6 generator

es6-generator.md

Why value from return statement is ignored when iterating through a generator

If you are iterating through an iterator, using a for ... of loop or something like Array.from, the return value is going to be ignored. In other words, the value included in the end-of-iteration object (whose property done is true) is ignored.

function *gen(){
 const val = yield 4;
 return val * 2;
}

for (let value of gen()) {
  console.log(value);
}

// output: 4

MDN function* documenation explained it very well:

A return statement in a generator, when executed, will make the generator done. If a value is returned, it will be passed back as the value. A generator which has returned will not yield any more values.

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Reference:

• StackOverflow question: https://stackoverflow.com/a/37202835/873234