转换值的运行类型

Question

是否可以创建一个不仅可以验证而且还可以转换给定值的 Runtype？

例如，检查正数：

import * as RT from "runtypes"
const PositiveOrFail = RT.Number.withConstraint(n => n >= 0)

但是，是否可以改为“默认”为一个值？

const PositiveOrClamp = RT.Number.???(n => (n >= 0) ? n : 0)

// Or another practical example:
const StringOrMissing = RT.String.optional().???(s => s ? s : "(missing)")

Answer 1

目前没有。不过，它有一个 PR 草案。

/**
 * example not currently released!!
 */
const Input = Record({
  date: String.withTransform(s => {
    const date = new Date(s);
    if (isNaN(date.valueOf())) throw new Error(`Invalid date string "${s}"`);
    else return date;
  }),
});
type Input = Static<typeof Input>;
// { date: Date; }

Input.check({ date: 'crap' });
// ValidationError: Failed transform: Error: Invalid date string "crap" in date

const input: Input = Input.check({ date: '1990-01-01' });
console.log(input.date.toUTCString());
// Mon, 01 Jan 1990 00:00:00 GMT

https://github.com/pelotom/runtypes/pull/191

https://github.com/pelotom/runtypes/issues/56