flow this 类型提示

问题背景

Appromal Admin 用的mobx进行状态管理

Mobx 官网推荐在异步场景下使用 flow 进行包装，进行状态更改

https://mobx.js.org/actions.html#using-flow-instead-of-async--await-

flow, like action, can be used to wrap functions directly. The above example could also have been written as follows:

TypeScript
Copy
import { flow } from "mobx"

class Store {
    githubProjects = []
    state = "pending"

    fetchProjects = flow(function* (this: Store) {
        this.githubProjects = []
        this.state = "pending"
        try {
            // yield instead of await.
            const projects = yield fetchGithubProjectsSomehow()
            const filteredProjects = somePreprocessing(projects)
            this.state = "done"
            this.githubProjects = filteredProjects
        } catch (error) {
            this.state = "error"
        }
    })
}

const store = new Store()
const projects = await store.fetchProjects()

The upside is that we don't need flowResult anymore, the downside is that this needs to be typed to make sure its type is inferred correctly.

问题

当时官网似乎还没有代码，因此我的写法是下面这样的

当使用上图的写法来写的时候，会丢失类型提示

解决方案

https://github.com/mobxjs/mobx/issues/1769#issuecomment-452703686

https://www.logicbig.com/tutorials/misc/typescript/function-this-parameter.html

从这个来看，是个TS的行为，不过没能寻找到出处