flow,如何从mixed类型转换为更具体的类型

一种方法是改进你收到的任何东西的类型,直到它符合你想要的形状。通常,我会制作一些基本的优化函数,并使用它们来构建更大的优化。

( Try )

// From libdef
type Locals = {
  [name: string]: mixed;
}

// Populated data
const locals: Locals = {
  version: 1.2,
  resources: {
    a: "abc",
    b: "def"
  }
};

// The type you want
type MyLocals = {
  version: number,
  resources: {
    // maybe this one is a map? idk
    [string]: string
  }
}

// Some basic refinement functions
const refineString = (x: mixed): string => {
  if (typeof x === 'string') {
    return x 
  }
  throw new Error("Not a string")
}

const refineNumber = (x: mixed): number => {
  if (typeof x === 'number') {
    return x 
  }
  throw new Error("Not a number")
}

const refineObj = (x: mixed): {[string]: mixed} => {
  if (x instanceof Object) {
    return x 
  }
  throw new Error("Not an object")
}

// More type-specifc refinement functions
const refineResources = (x: mixed): $ElementType<MyLocals, 'resources'> => {
  const anObj = refineObj(x)
  return Object.keys(anObj)
               .reduce((acc, k) => Object.assign(acc, { [k]: refineString(anObj[k]) }), {})
}

const refineMyLocals = (x: mixed): MyLocals => {
  const {version, resources} = refineObj(x)
  return {
    version: refineNumber(version),
    resources: refineResources(resources)
  }
}

// Now use them to assert a type
const myLocals: MyLocals = refineMyLocals(locals)
const version: number = myLocals.version;
const resources: {[string]: string} = myLocals.resources;

或者,如果libdef在 flow-typed 文件夹,进去换一下libdef。它将使该类型特定于您的项目,但如果您不需要 [name: string]: mixed 在代码中键入其他地方。

看来这里唯一的办法就是 refinement 逻辑。

if (typeof locals.version === "number") {
   const version: number = locals.version;
}
if (locals.resources instanceof Object) {
  const resources: {[string]: string} = locals.resources;
}

请注意,您也可以将数据本身转换为:

const version: number = Number(locals.version);

或定义新副本:

const resources: {[string]: string} = {...locals.resources};