Simple Type Guard

Installation

$ npm i -D simple-type-guard

Why Simple Type Guard?

Simple Type Guard takes the guess-work out of validating unknown variables against a type.

No longer will you have to carefully review your code to make sure you're validating every detail of an object to see if it fits.

Simple Type Guard will help you craft the template that perfectly matches your interface and warns you if something is missing or improperly defined.

Even better, you don't have to learn a new pattern or all the facets of a new library. The templates you match against are all standard Javascript.

All you have to do is provide a Generic type!

Examples

Primitives

All primitives will take the typeof value postfixed to Simple to compare against

import simpleTypeGuard, {
  SimpleString,
  SimpleBoolean,
  SimpleNumber,
} from 'simple-type-guard';

simpleTypeGuard<string>('hello world', SimpleString); // -> true

simpleTypeGuard<string>(1234, SimpleString); // -> false

simpleTypeGuard<boolean>(true, SimpleBoolean); // -> true

simpleTypeGuard<number>(0987, SimpleNumber); // -> true

Objects

Objects you can write just like you would an interface!

import simpleTypeGuard, { SimpleNumber } from 'simple-type-guard';

interface Foo {
  bar: number;
}

simpleTypeGuard<Foo>({ bar: 1234 }, { bar: SimpleNumber }); // -> true

simpleTypeGuard<Foo>({ bar: 'invalid string value' }, { bar: SimpleNumber }); // -> false

Arrays

Arrays will attempt to match every iteration of the passed in value to the first index of the template array.

import simpleTypeGuard, { SimpleNumber, SimpleArray } from 'simple-type-guard';

interface Foo {
  list: FooListItem[];
}

interface FooListItem {
  bar: number;
}

simpleTypeGuard<Foo>(
  { list: [{ bar: 1234 }, { bar: 1276 }, { bar: 12973 }] },
  {
    list: SimpleArray<FooListItem>({ bar: SimpleNumber }),
  }
); // -> true

simpleTypeGuard<Foo>(
  { list: [{ bar: 1234 }, { bar: 1276 }, { bar: 'invalid string value' }] },
  {
    list: [{ bar: SimpleNumber }],
  }
); // -> false

Enums

If you have a type consisting of a number of enums (ie type Color = 'red' | 'blue' | 'green'), consider using SimpleExactMatch. Every parameter will be matched against.

import simpleTypeGuard, { SimpleExactMatch } from 'simple-type-guard';

const colors = ['red', 'blue', 'green'];
type Color = typeof colors[number]; // 'red' | 'blue' | 'green'

simpleTypeGuard<Color>('red', new SimpleExactMatch(...colors)); // -> true

Unions

If you have a union consisting of multiple conflicting types, SimpleOr can be used to iterate through each possible type. Every parameter will be matched against.

NOTE: Booleans behave weirdly in Typescript when separating through unions. (boolean turns into true | false). To avoid issues, any time a boolean occurs within the SimpleOr, it must be the last value in the parameters.

For example: string | boolean | number -> new SimpleOr(SimpleString,SimpleNumber,SimpleBoolean)

import simpleTypeGuard, { SimpleOr } from 'simple-type-guard';

interface Car {
  model: string;
}

interface Person {
  company: string;
}

type Foo = Car | Person;

simpleTypeGuard<Foo>(
  { company: 'willowtree' },
  new SimpleOr({ model: SimpleString }, { company: SimpleString })
); // -> true

Functions

If you wanted a lot more control over how a type is validated, 'simple-type-guard' allows you to implement a function for a more specific validation test.

import simpleTypeGuard, { SimpleFunction } from 'simple-type-guard';

interface Foo {
  bar: 'one' | 'two' | 'three';
}

simpleTypeGuard<Foo>(
  { bar: 'one' },
  {
    bar: new SimpleFunction(
      (barVariable: unknown) =>
        ['one', 'two', 'three'].indexOf(barVariable) !== -1
    ),
  }
); // -> true

Optionals

Primitives

Primitive optionals are the same 'Simple' but with an 'Optional' postfix.

import simpleTypeGuard, { SimpleStringOptional } from 'simple-type-guard';

simpleTypeGuard<string | undefined>('hello world', SimpleStringOptional); // -> true

simpleTypeGuard<string | undefined>(undefined, SimpleStringOptional); // -> true

simpleTypeGuard<string | undefined>(1234, SimpleStringOptional); // -> false

This will also allow for null values.

...
simpleTypeGuard<string | null>(null, SimpleStringOptional); // -> true

Objects

Objects require using SimpleObjectOptional to indicate they may be undefined.

import simpleTypeGuard, {
  SimpleObjectOptional,
  SimpleNumber,
} from 'simple-type-guard';

interface Foo {
  bar: number;
}

simpleTypeGuard<Foo | undefined>(
  undefined,
  new SimpleObjectOptional<Foo>({ bar: SimpleNumber })
); // -> true

Arrays

import simpleTypeGuard, {
  SimpleNumber,
  SimpleArrayOptional,
} from 'simple-type-guard';

interface Foo {
  list?: FooListItem[];
}

interface FooListItem {
  bar: number;
}

simpleTypeGuard<Foo>(
  { list: undefined },
  {
    list: new SimpleArrayOptional<FooListItem[]>({ bar: SimpleNumber }),
  }
); // -> true

Options

throwErrorOnFailure (default: false)

When true, will throw an error when an incompatibility is found. This error will provide details on what went wrong.

import simpleTypeGuard, { SimpleString } from 'simple-type-guard';

interface Foo {
  bar: string;
}

simpleTypeGuard<Foo>(
  { bar: 173 },
  { bar: SimpleString },
  { throwErrorOnFailure: true }
); // ->
/**
 * Error: Invalid type detected at
 * "_root_.bar:
 * Expected "string"
 * Found "number"
 *
 * Variable Output: 173
 */