vue源码的疑惑

Question

无意中看见vue源码

export function initMixin (Vue: Class<Component>) { 
    Vue.prototype._init = function (options?: Object) {
    const vm: Component = this
    // a uid
    vm._uid = uid++

    ...
}

里面好多Vue: Class<Component> 和 const vm: Component = this，这些都是什么语法？

Answer 1

flow
没记错的话是 flow

Answer 2

https://flow.org/en/
flow类型检查。

Answer 3

楼主去查一下flow