How to advance an iterator.

[Jane Chen]

With the change of behavior in Iterator discussed here:

https://groups.google.com/forum/#!topic/v8-users/8LkrofVr0aA

If I have an iterator (natively defined) which supports for ... of loop, what is the equivalent of calling next to advance it?

I hope the following js example demonstrates what I mean:

> myIterable[Symbol.iterator] = function* () {yield 1;}
function* () {yield 1;}
> for (var k of myIterable) print(k);
1
> myIterable[Symbol.iterator];
function* () {yield 1;}
> myIterable[Symbol.iterator].next();
(shell):1: TypeError: myIterable[Symbol.iterator].next is not a function
myIterable[Symbol.iterator].next();
                            ^
TypeError: myIterable[Symbol.iterator].next is not a function
    at (shell):1:29

[Ben Noordhuis]

What version of V8 is that? It works in 4.6.

[Jane Chen]

4.6.88.  Just tried it in v8 shell.  myIterable[Symbol.iterator].next is undefined.

[Adam Klein]

You're missing a function call:

myIterable[Symbol.iterator]().next()  // note parens after the closing bracket

This follows the spec-internal method GetIterator: http://tc39.github.io/ecma262/#sec-getiterator

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[Jane Chen]

Ah, you are right.  Thanks!