Access of array per index isn't tracked

[javie5]

Version

3.0.1

Reproduction link

https://codepen.io/javie5/pen/jOrrYVx

Steps to reproduce

Click the 'add item' button

What is expected?

array item grouping rendering

What is actually happening?

Use 'for (index in array) {}' in computed or methods. When the array is initialized to empty, adding array items cannot refresh the view

[javie5]

I want to know why please

[edison1105]

@posva It's relate to for in , not for of.

[07akioni]

Currently in JS there is no trap for for in in Proxy. So it may not be consider as a bug but rather a constraint of JS.

https://stackoverflow.com/questions/38586471/how-to-control-property-enumeration-for-in-with-proxy-objects

tc39/ecma262#367

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Although the behavior of for in can't be proxyed, ownKeys would be called when execute for in.

[javie5]

@yyx990803 可以请教下为什么以下2种情况使用for in 视图依然可以同步更新吗:
1.在computed 中使用for in时,同时使用array.length

2.不使用数组,改用对象(初始化为空白对象)