Extract necessary functions from type-fest (#120)

source/types.ts

@@ -0,0 +1,49 @@
+// Extracted from https://github.com/sindresorhus/type-fest/blob/78019f42ea888b0cdceb41a4a78163868de57555/index.d.ts
+
+/**
+Matches any [primitive value](https://developer.mozilla.org/en-US/docs/Glossary/Primitive).
+*/
+export type Primitive =
+	| null
+	| undefined
+	| string
+	| number
+	| boolean
+	| symbol
+	| bigint;
+
+// TODO: Remove the `= unknown` sometime  in the future when most users are on TS 3.5 as it's now the default
+/**
+Matches a [`class` constructor](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes).
+*/
+export type Class<T = unknown, Arguments extends any[] = any[]> = new (...arguments_: Arguments) => T;
+
+/**
+Matches any [typed array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray), like `Uint8Array` or `Float64Array`.
+*/
+export type TypedArray =
+	| Int8Array
+	| Uint8Array
+	| Uint8ClampedArray
+	| Int16Array
+	| Uint16Array
+	| Int32Array
+	| Uint32Array
+	| Float32Array
+	| Float64Array
+	| BigInt64Array
+	| BigUint64Array;
+
+declare global {
+	interface SymbolConstructor {
+		readonly observable: symbol;
+	}
+}
+
+/**
+Matches a value that is like an [Observable](https://github.com/tc39/proposal-observable).
+*/
+export interface ObservableLike {
+	subscribe(observer: (value: unknown) => void): void;
+	[Symbol.observable](): ObservableLike;
+}