Deep Type Equals

Purpose

This package is a small, simple helper designed to perform deep type equality checks at runtime.

• It uses your existing types plus a typed reference object to confirm if input data matches the intended type.
• Works on simple types, literals, unions, arrays, objects and unknown.
• IN PROGRESS: a parser which will create your references automatically at runtime.

Usage

The helper takes two arguments, a reference object which contains the desired types, and the data which is to be checked.

If you are using TypeScript, you can either type the reference object OR pass the target type in as a type argument. This will ensure that the reference object is always compliant with the target type.

NOTE, this doesn't guarantee it is a complete reference object, it only confirms that it is a match for the type.

This may cause false negative results from deepTypeEquals as at runtime it is matching the types in the reference variable NOT the type definition.

Works on simple types, literals, unions, arrays, objects and unknown.

Set Up

npm i deep-type-equals
yarn add deep-type-equals

import deepTypeEquals, { createDeepTypeEquals, literal, optional, union, unknown } from "deep-type-equals";

Using a typed example object

type IExample = {
 id: number,
 value: string,
}

const reference: IExample = {
 id: 1,
 value: "value",
}

const result: boolean = deepTypeEquals( reference, input, options? ); // true or false

Using a type parameters

type IExample = {
 id: number,
 value: string,
}

const reference = {
 id: 1,
 value: "value",
}

const result: boolean = deepTypeEquals<IExample>( reference, input , options? ); // true or false

Curried

type MyType = {
 key: string,
 two: number,
}

const reference = {
 key: "test",
 two: 123,
};

const myTest = createDeepTypeEquals<MyType>( reference );
const result = myTest( data, options? ); // true or false;

Options

deepTypeEquals( reference, data, options? );

Available options:

• allowUnspecifiedObjectKeys: boolean, default false.
  • Skips the check for unexpected keys in the input data.
  • Potentially useful to skip checks for complex objects such a Express.request.

Basic Types

deepTypeEquals<string>( "test string", "string to test" ); // true
deepTypeEquals<string>( "test string", 12 ); //false

deepTypeEquals<number>( 123, 456 ); // true
deepTypeEquals<number>( 123, "456" ); // false

deepTypeEquals<boolean>( true, false ); // true
deepTypeEquals<boolean>( true, true ); // true
deepTypeEquals<boolean>( true, "true" ); //false

Arrays

deepTypeEquals<string[]>([ "test string" ], [ "input" ]); // true
deepTypeEquals<string[]>([ "test string" ], "input" ); // false

Objects

These will fail on unexpected keys, missing keys, and deeply checked mismatched types.

deepTypeEquals<{ key: string }>({ key: "test string" }, { key: "input" }); // true
deepTypeEquals<{ key: string }>({ key: "test string" }, "input" ); // false

Union Types

 type TestUnion = string | number;
 const reference = union<TestUnion>( "test string", 123 );

 deepTypeEquals<TestUnion>( reference, "string to test" ); // true;
 deepTypeEquals<TestUnion>( reference, true ); // false;

 type TestUnion = string | number;
 const reference = [ union<TestUnion>( "test string", 123 )];

 deepTypeEquals<TestUnion[]>( reference, [ "string to test" ]); // true;
 deepTypeEquals<TestUnion[]>( reference, [ "string to test", 243 ]); // true;
 deepTypeEquals<TestUnion[]>( reference, "string to test" ); // false;

Literals

deepTypeEquals( literal( "reference" ), "reference" ); // true
deepTypeEquals( literal( "reference" ), "other" ); // false

type Modes = "fast" | "slow";
const reference = union<Modes>( literal( "fast" ), literal( "slow" ));

deepTypeEquals( reference, "fast" ); // true
deepTypeEquals( reference, "slow" ); // true
deepTypeEquals( reference, "something else" ); // false

Optional Types

type MyType = {
 key: string,
 two?: number,
 three?: boolean,
}

const reference = { 
 key: "123",
 two: optional( 123 ),
 three: optional( false ),
};

const myTest = createDeepTypeEquals<MyType>( reference );

 myTest({ key: "test", two: 345, three: true }); // true
 myTest({ key: "test", two: 345 }); // true
 myTest({ key: "test" }); // true
 myTest({ two: 345, three: true }); // false

Unknown Types

 deepTypeEquals<TestUnion[]>( unknown(), [ "string to test" ]); // true;
 deepTypeEquals<TestUnion[]>( unknown(), "string to test" ); // true;
 deepTypeEquals<TestUnion[]>( unknown(), 123 ); // true;

Gaps

• No way to test if a value is a function yet.
• Readme and tests for undefined and null. These should work though just a reference values,
• No way to ensure that you provide a reference for all possible union values.

Bugs, Feedback & Contributions

I'd be glad to hear from you! So please provide any through issues, discussions or as a pull request above 😃