Static and runtime type assertion library with no dependencies

yarn add typanion

• Typanion can validate nested arbitrary data structures
• Typanion is type-safe; it uses type predicates
• Typanion allows you to derive types from your schemas
• Typanion can report detailed error reports

Compared to yup, Typanion has a better inference support for TypeScript + supports isOneOf. Its functional API makes it very easy to tree shake, which is another bonus (although the library isn't very large in itself).

Check the website for our documentation: mael.dev/typanion.

First define a schema using the builtin operators:

import * as t from 'typanion';
const isMovie = t.isObject({
    title: t.isString(),
    description: t.isString(),
});

Then just call the schema to validate any unknown value:

const userData = JSON.parse(input);
if (isMovie(userData)) {
    console.log(userData.title);
}

Passing a second parameter allows you to retrieve detailed errors:

const userData = JSON.parse(input);
const errors: string[] = [];
if (!isMovie(userData, {errors})) {
    console.log(errors);
}

You can also apply coercion over the user input:

const userData = JSON.parse(input);
const coercions: Coercion[] = [];
if (isMovie(userData, {coercions})) {
    // Coercions aren't flushed by default
    for (const [p, op] of coercions) op();
    // All relevant fields have now been coerced
    // ...
}

You can derive the type from the schema and use it in other functions:

import * as t from 'typanion';
const isMovie = t.isObject({
    title: t.isString(),
    description: t.isString(),
});
type Movie = t.InferType<typeof isMovie>;
// Then just use your alias:
const printMovie = (movie: Movie) => {
    // ...
};

Schemas can be stored in multiple variables if needed:

import * as t from 'typanion';
const isActor = t.isObject({
    name: t.isString();
});
const isMovie = t.isObject({
    title: t.isString(),
    description: t.isString(),
    actors: t.isArray(isActor),
});

Copyright © 2020 Mael Nison

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

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