Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

Awesome Lists | Featured Topics | Projects

https://github.com/gristlabs/ts-interface-checker

Runtime library to validate data against TypeScript interfaces.
https://github.com/gristlabs/ts-interface-checker

Last synced: 3 days ago
JSON representation

Runtime library to validate data against TypeScript interfaces.

Awesome Lists containing this project

README 

        
# ts-interface-checker



[![Build Status](https://travis-ci.org/gristlabs/ts-interface-checker.svg?branch=master)](https://travis-ci.org/gristlabs/ts-interface-checker)

[![npm version](https://badge.fury.io/js/ts-interface-checker.svg)](https://badge.fury.io/js/ts-interface-checker)



> Runtime library to validate data against TypeScript interfaces.



This package is the runtime support for validators created by

[ts-interface-builder](https://github.com/gristlabs/ts-interface-builder).

It allows validating data, such as parsed JSON objects received

over the network, or parsed JSON or YAML files, to check if they satisfy a

TypeScript interface, and to produce informative error messages if they do not.



## Installation



```bash

npm install --save-dev ts-interface-builder

npm install --save ts-interface-checker

```



## Usage



Suppose you have a TypeScript file defining an interface:

```typescript

// foo.ts

interface Square {

  size: number;

  color?: string;

}

```



The first step is to generate some code for runtime checks:

```bash

`npm bin`/ts-interface-builder foo.ts

```



It produces a file like this:

```typescript

// foo-ti.js

import * as t from "ts-interface-checker";



export const Square = t.iface([], {

  "size": "number",

  "color": t.opt("string"),

});

...

```



Now at runtime, to check if a value satisfies the Square interface:

```typescript

import fooTI from "./foo-ti";

import {createCheckers} from "ts-interface-checker";



const {Square} = createCheckers(fooTI);



Square.check({size: 1});                  // OK

Square.check({size: 1, color: "green"});  // OK

Square.check({color: "green"});           // Fails with "value.size is missing"

Square.check({size: 4, color: 5});        // Fails with "value.color is not a string"

```



Note that `ts-interface-builder` is only needed for the build-time step, and

`ts-interface-checker` is needed at runtime. That's why the recommendation is to npm-install the

former using `--save-dev` flag and the latter using `--save`.



## Checking method calls



If you have an interface with methods, you can validate method call arguments and return values:

```typescript

// greet.ts

interface Greeter {

  greet(name: string): string;

}

```



After generating the runtime code, you can now check calls like:

```typescript

import greetTI from "./greet-ti";

import {createCheckers} from "ts-interface-checker";



const {Greeter} = createCheckers(greetTI);



Greeter.methodArgs("greet").check(["Bob"]);     // OK

Greeter.methodArgs("greet").check([17]);        // Fails with "value.name is not a string"

Greeter.methodArgs("greet").check([]);          // Fails with "value.name is missing"



Greeter.methodResult("greet").check("hello");   // OK

Greeter.methodResult("greet").check(null);      // Fails with "value is not a string"

```



## Type suites



If one type refers to a type defined in another file, you need to tell the interface checker about

all type names when you call `createCheckers()`. E.g. given



```typescript

// color.ts

export type Color = RGB | string;

export type RGB = [number, number, number];

```



```typescript

// shape.ts

import {Color} from "./color";

export interface Square {

  size: number;

  color?: Color;

}

```



the produced files `color-ti.ts` and `shape-ti.ts` do not automatically refer to each other, but

expect you to relate them in `createCheckers()` call:

```typescript

import color from "./color-ti";

import shape from "./shape-ti";

import {createCheckers} from "ts-interface-checker";



const {Square} = createCheckers(shape, color);    // Pass in all required type suites.



Square.check({size: 1, color: [255,255,255]});

```



## Strict checking



You may check that data contains no extra properties. Note that it is not generally recommended as

it this prevents backward compatibility: if you add new properties to an interface, then older

code with strict checks will not accept them.



Following on the example above:

```typescript

Square.strictCheck({size: 1, color: [255,255,255], bg: "blue"});    // Fails with value.bg is extraneous

Square.strictCheck({size: 1, color: [255,255,255,0.5]});            // Fails with ...value.color[3] is extraneous

```



## Type guards



Standard `Checker` objects do the type checking logic, but are unable to make the TypeScript

compiler aware that an object of `unknown` type implements a certain interface.



Basic code:

```typescript

const unk: unknown = {size: 1, color: "green"};

// Type is unknown, so TypeScript will not let you access the members.

console.log(unk.size); // Error: "Object is of type 'unknown'"

```



With a `Checker` available:

```typescript

import fooTI from "./foo-ti";

import {createCheckers} from "ts-interface-checker";



const {Square} = createCheckers(fooTI);



const unk: unknown = {size: 1, color: "green"};



if (Square.test(unk)) {

  // unk does implement Square, but TypeScript is not aware of it.

  console.log(unk.size); // Error: "Object is of type 'unknown'"

}

```



To enable type guard functionality on the existing `test`, and `strictTest` functions, `Checker`

objects should be cast to `CheckerT<>` using the appropriate type.



Using `CheckerT<>`:

```typescript

import {Square} from "./foo";

import fooTI from "./foo-ti";

import {createCheckers, CheckerT} from "ts-interface-checker";



const checkers = createCheckers(fooTI) as {Square: CheckerT};



const unk: unknown = {size: 1, color: "green"};



if (checkers.Square.test(unk)) {

  // TypeScript is now aware that unk implements Square, and allows member access.

  console.log(unk.size);

}

```



## Type assertions



`CheckerT<>` will eventually support type assertions using the `check` and `strictCheck` functions,

however, this feature is not yet fully working in TypeScript.