root context bleeds into compiled function parameters

[rsbondi]

REPL

{{#each cats.filter(function(c) { return c.name!='Maru' }) as cat}}

compiles to

root.cats.filter(function(root.c) {return root.c.name!='Maru'}

[dxlbnl]

I'd say it's better to use a computed block for this.

{
  computed: {
    cats_filter: cats => cats.filter(...)
  }
}

[Rich-Harris]

Ah, yes. Hadn't anticipated function expressions inside tags. It could be made to work — would need to do an initial pass on the code to annotate it with scopes so that we can identify that c is a local variable and leave it alone.

The much simpler alternative would be to disallow [arrow] function expressions in tags. That would have a theoretical performance benefit (the mapping function would only need to be created once), though it does mean you would need to add a computed property as per @neoel's example, or add a helper:

{{#each cats.filter(notMaru) as cat}}
  <!-- ... -->
{{/each}}

<script>
  export default {
    helpers: {
      notMaru: cat => cat.name !== 'Maru'
    }
  };
</script>

Not totally sure which is the best option!

[PaulBGD]

@Rich-Harris I think it'd be worth to add support for it, but adding it as a helper seems to be the best option for performance + reusability.

[Rich-Harris]

This is fixed in 1.9.1 — thanks