# Embedding V8 in NativeScript - Vladimir Mutafov
###### tags: `jsdc2019`

{%hackmd @JSDC-tw/2019-announcement %}

[講者 github](https://github.com/vmutafov)

## [NativeScript](https://www.nativescript.org/)
Open source framework for building truly native mobile apps with Angular, Vue.js, TypeScript, or JavaScript.

### NativeScript Magic
- JS code
- N Runtime
- V8

### Application launch
啟動 V8 -> 讀取 Metadata > 觸發 Callbacks

### JNI(Java Native Interface)
V8 (NativeScript Runtime) <=> ART (Android Runtime)

v8:OobjectTemplate::

### Marshalling

java.lang.String !== string

Convert data type between Java and Javascript.

Java objects are proxied to special JS objects.

### Objects lifecycle

- garbage collection (Both V8 and Android Runtime have)

**problem:** garbage collector doesn't know when should stop so it need sync.

Sync by nativescript runtime

#### Out of Memory exceptions
JS proxy object is smaller

1. v8::Isolate::
2. forcing garbage collection (not good)
3. `releaseNativeCounterpart(jsImage)`

#### Multithreading
Mobile Application need 60 fps
Worker threads for CPU intensive work (isolate in v8)
one islolation = multiple contexts

#### Context

Worker Thread = isolate

### SnapShot

- FS request (performance issue, very slow)
- solution: bundle
- snapshot limitation: build snapshot at build time → no Android information (e.g. android.os.Build.Version.SDK.INT ⇒ use getter to avoid error!)

#### loading snapshots

**problem:** No Native API

@StanimiraVlaeva
@VladimirMutafov

### Q&A

2. How to Debugging
3. Marshalling
4. v8 provide native Interface APIs for UI?

## Example (iOS)

1. [下載 Nativescript Preview](https://apps.apple.com/tw/app/nativescript-preview/id1264484702)
2. [去這裡隨便選個 Sample](https://market.nativescript.org/?tab=samples&framework=vue&category=all_samples&_ga=2.57672618.1022828759.1572057055-1905761369.1572057055)
3. 用 Nativescript Preview 掃 QR Code
4. 開始開發！