Type Guard Utils -- WIP -- Use at your own risk

Rxjs Operators

Typescript Method Decorators

Utility functions/factories

Detailed function descriptions

typeGuardCheckOperator

An an operator to use with rxjs observables. Could be used to check the type on any state of an observable.

The best use case for this would be on the edges of your application such as request to external APIs. This would help with both verifying that the you defined the correct types for the returned values. This would also help to catch if the data type returned from an API changes.

Kind: global variable

| Param | Description | | --- | --- | | typeChecker | A function that acts as a type guard. Accepts the item in and returns a boolean for if its valid | | expectArray | Apply the typeChecker to an array of items instead of individual item. | | invalidTypeCallback | Callback for if typeChecker(item) returns false | | validTypeCallback | Callback for if typeChecker(item) returns true |

typeGuardMapOperator

Same as typeGuardCheckOperator expect that the observable gets emitted to the return value from either the invalidTypeCallback or the validTypeCallback. If either callback is omitted the stream is re-emitted when that callback is called.

Kind: global variable

checkWithTypeGuard(typeChecker, expectArray, invalidTypeCallback, validTypeCallback, mapInsteadOfCheck)

A method decorator to check return type.

For Observables: Wraps the typeGuardMapOperator.

For Promises and non-async values: Wraps internal handleTypeGuardValidation function.

Can handle () => ReturnType | <Promise> | <Observable>

Kind: global function

| Param | Default | Description | | --- | --- | --- | | typeChecker | | A function that acts as a type guard. Accepts the item in and returns a boolean for if its valid | | expectArray | false | Apply the typeChecker to an array of items instead of individual item | | invalidTypeCallback | | Callback for if typeChecker(item) returns false | | validTypeCallback | | Callback for if typeChecker(item) returns true | | mapInsteadOfCheck | false | If true the return type gets mapped to the return from either the invalidTypeCallback or validTypeCallback. Default is that the return value is unchanged. |

validatorFactory(typeChecker, expectArray, invalidTypeCallback, validTypeCallback)

The validatorFactory returns a validator function that can be used to do runtime type checks for a certain type.

The invalidTypeCallback and validTypeCallbacks null/undefined or a some value. If null/undefined the original value is returned from the validator function, if any other value is return that value is also returned by the validator.

Example: let cars = 0; const logInvalidType = (car) => { postToSomeLoggingService(car) } const incrementCarCount = () => { cars++ }

const carsValidator = validatorFactory(isCar, true, logInvalidCar, incrementCarCount)

In cases where invalidTypeCallback or validTypeCallback don't return anything we can use this to check a value and also a return value.

To check an existing value: const car = {...} carValidator(car)

To check a return value, you can just use the validator as a higher order function:

const car = carValidator(getNextCar())

Kind: global function

| Param | Description | | --- | --- | | typeChecker | A function that acts as a type guard. Accepts the item in and returns a boolean for if its valid | | expectArray | Apply the typeChecker to an array of items instead of individual item. | | invalidTypeCallback | Callback for if typeChecker(item) returns false | | validTypeCallback | Callback for if typeChecker(item) returns true |

typeGuardOperatorFactory(operator)

Mostly for internal use but exposing incase anyone wants to do anything other than the predefined operators.

Kind: global function

| Param | Description | | --- | --- | | operator | Accepts an rxjs operator |