Composition API reference (#97)

* feat: added composition API reference

* fix: changed define component link

* Update src/api/composition-api.md

Co-authored-by: Rahul Kadyan <hi@znck.me>

* Update src/api/composition-api.md

Co-authored-by: Rahul Kadyan <hi@znck.me>

* feat: added composition API reference

* fix: changed define component link

* fix: move arguments above usecases

* feat: added example for attrs destructuring

* fix: fixed `this` usage explanation

* feat: added explanation about inline event handler

* fix: added example to `isReactive`

* fix: grammar

* fix: grammar

* fix: removed raw values mention

* Addressed reviewers comments

* feat: moved reactivity APIs

* feat: moved reactivity utilities

* feat: separated advanced reactivity apis

* fix: fixed indentation

* fix: refactored reactivity API structure

* feat: added links to composition API

* fix: renamed proxy APIs to basic

* fix: fixed reactive typing

* fix: addressed reviewers comments

* fix: added async onInvalidate

* feat: added example for generic with unknown type

* fix: fixed cleanup example

* fix: removed warning

Co-authored-by: Rahul Kadyan <hi@znck.me>

src/.vuepress/config.js

@@ -80,10 +80,20 @@ const sidebar = {
         '/api/options-misc'
       ]
     },
-    '/api/instance-properties.md',
-    '/api/instance-methods.md',
-    '/api/directives.md',
-    '/api/special-attributes.md'
+    '/api/instance-properties',
+    '/api/instance-methods',
+    '/api/directives',
+    '/api/special-attributes',
+    {
+      title: 'Reactivity API',
+      collapsable: false,
+      children: [
+        '/api/basic-reactivity',
+        '/api/refs-api',
+        '/api/computed-watch-api'
+      ]
+    },
+    '/api/composition-api'
   ]
 }
 

src/api/basic-reactivity.md

@@ -0,0 +1,173 @@
+# Basic Reactivity APIs
+
+> This section uses [single-file component](TODO: SFC) syntax for code examples
+
+## `reactive`
+
+Returns a reactive copy of the object.
+
+```js
+const obj = reactive({ count: 0 })
+```
+
+The reactive conversion is "deep"—it affects all nested properties. In the [ES2015 Proxy](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy) based implementation, the returned proxy is **not** equal to the original object. It is recommended to work exclusively with the reactive proxy and avoid relying on the original object.
+
+### Typing
+
+```ts
+function reactive<T extends object>(target: T): UnwrapNestedRefs<T>
+```
+
+## `readonly`
+
+Takes an object (reactive or plain) or a [ref](./refs-api.html#ref) and returns a readonly proxy to the original. A readonly proxy is deep: any nested property accessed will be readonly as well.
+
+```js
+const original = reactive({ count: 0 })
+
+const copy = readonly(original)
+
+watchEffect(() => {
+  // works for reactivity tracking
+  console.log(copy.count)
+})
+
+// mutating original will trigger watchers relying on the copy
+original.count++
+
+// mutating the copy will fail and result in a warning
+copy.count++ // warning!
+```
+
+## `isProxy`
+
+Checks if an object is a proxy created by [`reactive`](#reactive) or [`readonly`](#readonly).
+
+## `isReactive`
+
+Checks if an object is a reactive proxy created by [`reactive`](#reactive).
+
+```js
+import { reactive, isReactive } from 'vue'
+export default {
+  setup() {
+    const state = reactive({
+      name: 'John'
+    })
+    console.log(isReactive(state)) // -> true
+  }
+}
+```
+
+It also returns `true` if the proxy is created by [`readonly`](#readonly), but is wrapping another proxy created by [`reactive`](#reactive).
+
+```js{7-15}
+import { reactive, isReactive, readonly } from 'vue'
+export default {
+  setup() {
+    const state = reactive({
+      name: 'John'
+    })
+    // readonly proxy created from plain object
+    const plain = readonly({
+      name: 'Mary'
+    })
+    console.log(isReactive(plain)) // -> false
+
+    // readonly proxy created from reactive proxy
+    const stateCopy = readonly(state)
+    console.log(isReactive(stateCopy)) // -> true
+  }
+}
+```
+
+## `isReadonly`
+
+Checks if an object is a readonly proxy created by [`readonly`](#readonly).
+
+## `toRaw`
+
+Returns the raw, original object of a [`reactive`](#reactive) or [`readonly`](#readonly) proxy. This is an escape hatch that can be used to temporarily read without incurring proxy access/tracking overhead or write without triggering changes. It is **not** recommended to hold a persistent reference to the original object. Use with caution.
+
+```js
+const foo = {}
+const reactiveFoo = reactive(foo)
+
+console.log(toRaw(reactiveFoo) === foo) // true
+```
+
+## `markRaw`
+
+Marks an object so that it will never be converted to a proxy. Returns the object itself.
+
+```js
+const foo = markRaw({})
+console.log(isReactive(reactive(foo))) // false
+
+// also works when nested inside other reactive objects
+const bar = reactive({ foo })
+console.log(isReactive(bar.foo)) // false
+```
+
+::: warning
+`markRaw` and the shallowXXX APIs below allow you to selectively opt-out of the default deep reactive/readonly conversion and embed raw, non-proxied objects in your state graph. They can be used for various reasons:
+
+- Some values simply should not be made reactive, for example a complex 3rd party class instance, or a Vue component object.
+
+- Skipping proxy conversion can provide performance improvements when rendering large lists with immutable data sources.
+
+They are considered advanced because the raw opt-out is only at the root level, so if you set a nested, non-marked raw object into a reactive object and then access it again, you get the proxied version back. This can lead to **identity hazards** - i.e. performing an operation that relies on object identity but using both the raw and the proxied version of the same object:
+
+```js
+const foo = markRaw({
+  nested: {}
+})
+
+const bar = reactive({
+  // although `foo` is marked as raw, foo.nested is not.
+  nested: foo.nested
+})
+
+console.log(foo.nested === bar.nested) // false
+```
+
+Identity hazards are in general rare. However, to properly utilize these APIs while safely avoiding identity hazards requires a solid understanding of how the reactivity system works.
+:::
+
+## `shallowReactive`
+
+Creates a reactive proxy that tracks reactivity of its own properties but does not perform deep reactive conversion of nested objects (exposes raw values).
+
+```js
+const state = shallowReactive({
+  foo: 1,
+  nested: {
+    bar: 2
+  }
+})
+
+// mutating state's own properties is reactive
+state.foo++
+// ...but does not convert nested objects
+isReactive(state.nested) // false
+state.nested.bar++ // non-reactive
+```
+
+## `shallowReadonly`
+
+Creates a proxy that makes its own properties readonly, but does not perform deep readonly conversion of nested objects (exposes raw values).
+
+```js
+const state = shallowReadonly({
+  foo: 1,
+  nested: {
+    bar: 2
+  }
+})
+
+// mutating state's own properties will fail
+state.foo++
+// ...but works on nested objects
+isReadonly(state.nested) // false
+state.nested.bar++ // works
+```