feat: add Primitive and Falsey (#70)

As requested in #69 (comment)

README.md

@@ -57,6 +57,11 @@ Issues can be funded by anyone and the money will be transparently distributed t
 
 # Table of Contents
 
+## Aliases
+
+* [`Primitive`](#primitive)
+* [`Falsey`](#falsey)
+
 ## Operations on sets
 
 * [`SetIntersection<A, B>`](#setintersectiona-b-same-as-extract)
@@ -209,6 +214,22 @@ Extract subset `B` from set `A`
 
 ---
 
+## Aliases
+
+### `Primitive`
+
+The primitive types in TypeScript
+
+[⇧ back to top](#aliases)
+
+### `Falsey`
+
+The falsey values in TypeScript, except NaN which cannot be represented as a type literal
+
+[⇧ back to top](#aliases)
+
+---
+
 ## Operations on objects
 
 ### `FunctionKeys<T>`

src/__snapshots__/mapped-types.spec.ts.snap

@@ -82,6 +82,8 @@ exports[`DeepRequired testType<ReturnType<DeepRequired<NestedFunctionProps>['fir
 
 exports[`Diff testType<Diff<Props, NewProps>>() 1`] = `"Pick<Props, \\"name\\" | \\"visible\\">"`;
 
+exports[`Falsey testType<Falsey>() 1`] = `"Falsey"`;
+
 exports[`FunctionKeys testType<FunctionKeys<MixedProps>>() 1`] = `"\\"setName\\""`;
 
 exports[`Intersection testType<Intersection<Props | NewProps, DefaultProps>>() 1`] = `"Pick<Props, \\"age\\"> | Pick<NewProps, \\"age\\">"`;
@@ -104,6 +106,8 @@ exports[`Overwrite testType<Overwrite<Props, NewProps>>() 1`] = `"Pick<Pick<Prop
 
 exports[`PickByValue testType<PickByValue<Props, string | number>>() 1`] = `"Pick<Props, \\"name\\" | \\"age\\">"`;
 
+exports[`Primitive testType<Primitive>() 1`] = `"Primitive"`;
+
 exports[`PromiseType testType<PromiseType<Promise<string>>>() 1`] = `"string"`;
 
 exports[`ReadonlyKeys testType<ReadonlyKeys<ReadWriteProps>>() 1`] = `"\\"a\\""`;

src/index.ts

@@ -24,12 +24,14 @@ export {
   DeepNonNullable,
   DeepPartial,
   Diff,
+  Falsey,
   FunctionKeys,
   Intersection,
   NonFunctionKeys,
   NonUndefined,
   Omit,
   Overwrite,
+  Primitive,
   PromiseType,
   SetComplement,
   SetDifference,

src/mapped-types.spec.ts

@@ -1,5 +1,7 @@
 import { testType } from '../utils/test-utils';
 import {
+  Primitive,
+  Falsey,
   SetIntersection,
   SetDifference,
   SetComplement,
@@ -48,6 +50,18 @@ type ReadWriteProps = { readonly a: number; b: string };
  * Tests
  */
 
+// @dts-jest:group Primitive
+it('Primitive', () => {
+  // @dts-jest:pass:snap
+  testType<Primitive>();
+});
+
+// @dts-jest:group Falsey
+it('Falsey', () => {
+  // @dts-jest:pass:snap
+  testType<Falsey>();
+});
+
 // @dts-jest:group SetIntersection
 it('SetIntersection', () => {
   // @dts-jest:pass:snap

src/mapped-types.ts

@@ -1,8 +1,26 @@
 /**
- * Credits to all the people who given inspiration and shared some very usefull code snippets
+ * Credits to all the people who given inspiration and shared some very useful code snippets
  * in the following github issue: https://github.com/Microsoft/TypeScript/issues/12215
  */
 
+/**
+ * Primitive
+ * @desc The primitive types in TypeScript
+ * @example
+ *   // Expect: object
+ *   // type ResultStripPrimitives = Exclude<string | object, Primitive>
+ */
+export type Primitive = number | boolean | string | symbol;
+
+/**
+ * Falsey
+ * @desc The falsey values in TypeScript, except NaN
+ * @example
+ *   // Expect: "a" | "b"
+ *   // type ResultCompact = Exclude<'a' | 'b' | undefined | false, Falsey>;
+ */
+export type Falsey = null | undefined | false | 0 | '';
+
 /**
  * SetIntersection (same as Extract)
  * @desc Set intersection of given union types `A` and `B`