diff --git a/src/types/global.d.ts b/src/types/global.d.ts
new file mode 100644
index 0000000..4a3191a
--- /dev/null
+++ b/src/types/global.d.ts
@@ -0,0 +1,24 @@
+export {};
+
+declare global {
+  /**
+   * Allows extracting all possible values of another type.
+   */
+  type ValueOf<T> = T[keyof T];
+
+  /**
+   * Like Partial utility type, only this allows specifying select keys
+   * to be made optional instead of all keys.
+   */
+  type Optional<T, K extends keyof T> = Partial<Pick<T, K>> & Omit<T, K>
+
+  /**
+   * A slightly nicer way of defining nullable types.
+   */
+  type Nullable<T> = T | null;
+
+  /**
+   * Replace the type for specified keys of a type.
+   */
+  type Replace<T, K extends keyof T, R> = Omit<T, K> & { [key in K]: R };
+}