Runtime library to validate data against TypeScript interfaces.
This package is the runtime support for validators created by 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.
bash
npm install --save-dev ts-interface-builder
npm install --save ts-interface-checker
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.
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" ```
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]}); ```
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
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 {Square} = createCheckers(fooTI) as {Square: CheckerT
const unk: unknown = {size: 1, color: "green"};
if (Square.test(unk)) { // TypeScript is now aware that unk implements Square, and allows member access. console.log(unk.size); } ```
CheckerT<> will eventually support type assertions using the check and strictCheck functions,
however, this feature is not yet fully working in TypeScript.