Odd behaviour with setTimeout.

[sustained]

Version

2.6.7

Reproduction link

https://jsfiddle.net/sustained/zody8sf4/

Steps to reproduce

Just look at the code/result for the test-3 component.

What is expected?

I'd personally expect test-3 to work, if test-2 and test-1 do.

And I honestly have no idea why test-5 works at all, especially if test-3 doesn't.

Something seems a bit weird here.

What is actually happening?

It doesn't.

[sirlancelot]

The created() hook is called before render() so even though the property test.foo is not reactive, it exists by the time the component is rendered except when deferred via setTimeout().

Hopefully this explains the inconsistency you're seeing. The best practice has always been to use Vue.set() or vm.$set() when creating new properties as shown in the Change Detection Caveats section of the guide.