What problem does this feature solve?

The reactivity package lacks a way to determine the shallow type, so add an isShallow method like what isReadonly do.

I want to use isShallow in my project to judge if a reactive is of type shallow.

What does the proposed API look like?

import { isShallow, shallowReactive } from 'vue'
const foo = shallowReactive({ test: 1 })
if (isShallow(foo)) {
  // ... do something
}

see #3045

What is the usecase?

I still think that this requires a real use case, rather than a simple code demonstration. I don’t see what scenarios users need to care about whether the data is shallow or not.

I still think that this requires a real use case, rather than a simple code demonstration. I don’t see what scenarios users need to care about whether the data is shallow or not.

其实我觉得isReadonly和isShallow类似

My use case is a clone function where I want to accept any reactive object and return the a new object of the exact same type.

const source = reactive({ hello: 'world' })
const copy = clone(source)

source.hello = 'bob'

copy.hello // 'world'

But there's an issue if you pass in something that is shallow.

const source = shallowReactive({ hello: ref('world') })
const copy = clone(source)

source.hello // RefImp
copy.hello // 'world'

This happens because I can check if the source is reactive, but I cannot check if it is shallow. So it ends up returning reactive instead of shallowReactive.

function clone(source) {
  let copy
  // code that actually does the data copying
  
  if(isReactive(source) {
    return reactive(copy)
  }
}

But what I'd like to be able to do is

function clone(source) {
  let copy
  // code that actually does the data copying

  if(isReactive(source) {
    return isShallow(source) ? shallowReactive(copy) : reactive(copy)
  }
}

isShallow() was added in https://github.com/vuejs/core/commit/9fda9411ec92dc703288b229106116dd0f16e5e7. It has been available since 3.2.28.

isShallow is exported now, but didn't introduced in the docs. Should we make it public?