Micro letter applet underlying principles and operation mechanism of learning articles

Reference Documents

Only by mvvm template syntax dynamically change the page, do not support the operation of BOM
Compilation process:
- wcc compiled executable file generated .xml js script, the incoming js script right path, got a virtual dom tree.
WAWebview.js
- wx is registered under api, eventually calling WeixinJSBrige method.
- wxparser object dom to provide mapping between wx element, the element operation management, event management functions
- Assembly portion implemented using native code, for example: wx-video, wx-canvas, wx-map, wx-textarea, etc.
- native assembly suspended above webview, most of the components used to achieve the front end.
WeixinJSBridge
- wx.request actual call WeixinJSBridge, call distinguish the browser environment.
WAService.js
- wx API; APP (), Page (); page has the scope to provide a modular; data binding; event distribution; life cycle; routing;
Specific architecture composed of two webview: UI layer, Logic layer
- UI layer runs in a first webview, perform the operation and interaction DOM event response, which is the content code and compiled WAWebview
- Logic layer runs in a separate JS engine: ios: JavaScriptCore, android: x5, development tools:? Nwjs chrome kernel
- Logical layer comprises a service code and WAService.js
- By WeixinJSBridge, =>? Interaction between (native) between two layers

A program has multiple view, which is more webview
A small program has only one service process, but also a webview, run the program life cycle inherent in the background
两者都通过WeixinJSBridge和后台通信
view模块和service模块均使用postMessage进行通信
contentScript.js的代码提供了message消息到chrome.runtime通信接口的转换

使用客户端提供的JavaScript引擎, 沙箱只是单纯的提供JavaScript解释环境, 没有浏览器任何接口
小程序的基础库分别注入到视图层和逻辑层运行
- 视图层: 提供各类组件来组建界面
- 逻辑层: 提供各种API来处理逻辑
- 处理数据绑定, 组件系统, 事件系统, 通信系统等一系列框架
- 基础库不会打包到某个小程序代码, 会提前内置在微信客户端
基于shadow dom模型
启动机制
- 热启动: 打开过小程序, 在一定时间内再次打开
- 冷启动: 首次打开或者被微信销毁后打开
- 没有重启概念
- 进入后台后, 维持一段时间的运行后被销毁, 目前是五分钟.
- 短时间(5s), 连续收到两次系统内存告警, 会进行小程序销毁.
更新机制
- 冷加载读取缓存/检查更新
- 热加载直接后台切前台
- 冷启动时发现有新版本, 会异步下载新版本的代码包, 并同时用客户端本地的包进行启动
- 即新版小程序发布后, 需要经历两次冷启动, 才会应用
- 如果需要新版本, 可以使用指定API进行更新
setData
- webview和jsCore是单独模块
- 两边都通过evaluateJavaScript实现, 即用户传输的数据.
- 需要将其转换成一份JS脚本, 通过执行脚本进行执行

未启动时更新
- 微信客户端有若干个时机检查本地缓存的小程序有没有新版本, 有静默升级
- 发布新版本后, 无法同步所有的用户, 24小时, 同步所有新版本信息到用户手机
- 下次进行冷启动时, 先更新最新版本再打开.
启动时更新
- 每次冷启动都会检查更新, 异步下载最新的版本的代码包, 但会用本地的包进行启动
- 新版本在下一次冷启动时, 应用.

Why small micro-channel two webview program, which has to logic thread is running in the webview, how there is no window object?
How to write the introduction JS explained it in an operating system environment?
What shadowdom that?