Difference between yield * and yielding in a for..of loop?

Question

Given the following two pieces of code:

function * gen(g) {
 for (const value of g) {
 yield value;
 }
}

and

function * gen(g) {
 yield * g;
}

is there any difference in the behavior? As far as I can tell these are behaviorally identical. I'm having trouble seeing the value of the yield * syntax. It's more limiting than just iterating over the iterable in a for..of loop, and less obvious in what it does when reading it (in my opinion).

• Anonymous: From what I see here, it looks like they're pretty much the same except that yield* is an expression. The only other differences are that yield* is quicker to write, and I would guess it has been optimized somewhat.
• Felix Kling: @Anonymous: yield ... is an expression too.
• Anonymous: @FelixKing But for ... of is a statement, so you can do var x = yield* ..., but not var x = for ....

Answer 1

Here's the ExploringJS explanation of the difference, which is very exhaustive. The answer is typically, yes, they're equivalent, but there are some small differences. The most notable difference is that return values are forwarded by yield * but not by iterating and yielding.

Here's an example. The difference is minor.

• Elliot E: Thanks, exactly the kind of thing I was looking for.