can.batch.start/stop causes can.List with length>1 to render last element twice

[stevenvachon]

{{#each arr}} {{.}} {{/each}}

for (var i=1; i<=2; i++) {
    this.arr.push(i);
}

will produce 1,2, however:

can.batch.start();
for (var i=1; i<=2; i++) {
    this.arr.push(i);
}
can.batch.stop();

will produce 1,2,2.

?

http://jsfiddle.net/prometh/34YZP/

[stevenvachon]

Updated fiddle with can.stache. The issue persists.

[gsmeets]

ah, this might explain why I am having my last item rendered twice in a select list.

[justinbmeyer]

@stevenvachon great catch. @cklanac , this is maybe because two add events are fired and #each's add and remove handlers (https://github.com/bitovi/canjs/blob/master/view/live/live.js#L159) are not checking the batchNum.

You can see how https://github.com/bitovi/canjs/blob/master/compute/compute.js#L233 checks the batch num.

... however on second thought, that doesn't seem like the likely problem. Maybe the arguments are not right for the add event.

[cklanac]

@stevenvachon Thanks for submitting the issues. This issue is caused by the {{#if breaks.length}} helper interacting with the batched update and {{#each breaks}} helper. We've a fix to the next release.

In the meantime, you can workaround the issue by removing the .length from the if helper - simply {{#if breaks}}... {{/if}}, or change {{#each breaks}} helper to simply {{#breaks}}{{.}}{{/breaks}}.

http://canjs.com/docs/can.stache.Sections.html#section_Iteration

http://jsfiddle.net/cklanac/wfm6k20r/