如何使用/定义具有流类型检查的枚举？

Question

我正在尝试迁移现有的代码库以使用Flow.由于这个项目在没有Flow的情况下开始,我使用了一个非常典型的JS模式用于枚举等.

以下是我想要的一些定义

export const LOAN_STATUS  = {
  PENDING: 'pending',
  CURRENT: 'current',
  DUE: 'due',
  OVERDUE: 'overdue',
  PENDING_PAYMENT: 'pending_payment',
  CHARGED_OFF: 'charged_off',
  VOIDED: 'voided',
  DISPUTED: 'disputed',
  REFUNDED: 'refunded',
  SETTLED: 'settled',
}

export const ACTIVE_LOAN_STATUS = [
  LOAN_STATUS.OVERDUE,
  LOAN_STATUS.CURRENT,
  LOAN_STATUS.DUE,
  LOAN_STATUS.PENDING_PAYMENT,
]

Flow工作正常,直到我导入此文件,它说我需要添加类型注释.这看起来很奇怪 - 为什么我必须注释完全静态且易于推断的对象？

有没有办法将其类型定义为"静态"或"文字"？

那么我就开始考虑如何为此添加注释.我的第一个想法就是{[key: string]: string}和Array<string>.Flow有效,但我意识到这些类型定义完全没用.那么我尝试另一种方法:

type LoanStatusValues =
  'pending' |
  'current' |
  'due' |
  'overdue' |
  'pending_payment' |
  'charged_off' |
  'voided' |
  'disputed' |
  'refunded' |
  'settled'

type LoanStatusKeys =
  'PENDING' |
  'CURRENT' |
  'DUE' |
  'OVERDUE' |
  'PENDING_PAYMENT' |
  'CHARGED_OFF' |
  'VOIDED' |
  'DISPUTED' |
  'REFUNDED' |
  'SETTLED'

type ActiveLoanStatus = 
"current" |
"due" |
"overdue" |
"pending_payment"

我使用类型注释{[key: LoanStatusKeys]: LoanStatusValues}和Array<ActiveLoanStatus>.但即便是这些注释也忽略了这是静态的事实!

看起来很奇怪,我不得不写这么多重复的代码.然后,如果我想转换为Flow,我实际上无法使用JS中的类型.例如,我可能这样做:

if (defs.ACTIVE_LOAN_STATUS.indexOf(loan.status) !== -1) {

}

现在,如果我想使用Flow类型,我不能做这样的事情:

type ActiveLoanStatus = 
  "current" |
  "due" |
  "overdue" |
  "pending_payment"

if (loan.status isTypeOf ActiveLoanStatus) {

}

那么我该如何使用这些静态枚举？我一定是做错了!

Answer 1

以下是实现此目的的最简洁方法:

const activeLoanStatuses = {
  current: 'current',
  due: 'due',
  overdue: 'overdue',
  pending_payment: 'pending_payment'
};

const otherLoanStatuses = {
  pending: 'pending',
  charged_off: 'charged_off',
  voided: 'voided',
  disputed: 'disputed',
  refunded: 'refunded',
  settled: 'settled',
};

type ActiveLoanStatus = $Keys<typeof activeLoanStatuses>;
type LoanStatus = $Keys<typeof otherLoanStatuses> | ActiveLoanStatus;

const activeLoanStatusesMap: { [key: LoanStatus]: ?ActiveLoanStatus} = activeLoanStatuses;

if (activeLoanStatusesMap[loan.status]) {

}

Answer 2

要使用流表达枚举,可以将$ Values实用程序与冻结对象类型结合使用:

export const LOAN_STATUS = Object.freeze({
  PENDING: 'pending',
  CURRENT: 'current',
  DUE: 'due',
  OVERDUE: 'overdue',
  PENDING_PAYMENT: 'pending_payment',
  CHARGED_OFF: 'charged_off',
  VOIDED: 'voided',
  DISPUTED: 'disputed',
  REFUNDED: 'refunded',
  SETTLED: 'settled',
});

type LoanStatus = $Values<typeof LOAN_STATUS>;

export const ACTIVE_LOAN_STATUS: LoanStatus[] = [
  LOAN_STATUS.OVERDUE,
  LOAN_STATUS.CURRENT,
  LOAN_STATUS.DUE,
  LOAN_STATUS.PENDING_PAYMENT,
]

这适用于0.60.0版本.