@@ -0,0 +1,22 @@
+export declare class Either<L = unknown, R = unknown> {
+  constructor(params: { left?: L | null; right?: R | null });
+
+  static left<L>(value: L): Either<L, null>;
+
+  static right<R>(value: R): Either<null, R>;
+
+  get left(): L | null;
+
+  get right(): R | null;
+
+  isLeft(): boolean;
+
+  isRight(): boolean;
+
+  map<U>(fn: (value: R) => U): Either<L, U>;
+
+  match<T>(
+    leftFn: (left: L) => T,
+    rightFn: (right: R) => T
+  ): T;
+}
@@ -0,0 +1,60 @@
+'use strict';
+
+class Either {
+  #left = null;
+  #right = null;
+
+  constructor({ left = null, right = null }) {
+    this.#left = left;
+    this.#right = right;
+  }
+
+  static left(value) {
+    return new Either({ left: value, right: null });
+  }
+
+  static right(value) {
+    return new Either({ left: null, right: value });
+  }
+
+  get left() {
+    return this.#left;
+  }
+
+  get right() {
+    return this.#right;
+  }
+
+  isLeft() {
+    return this.#left !== null;
+  }
+
+  isRight() {
+    return this.#right !== null;
+  }
+
+  map(fn) {
+    if (this.#right === null) return this;
+    return Either.right(fn(this.#right));
+  }
+
+  match(leftFn, rightFn) {
+    const isRight = this.#right !== null;
+    return isRight ? rightFn(this.#right) : leftFn(this.#left);
+  }
+}
+
+// Usage
+
+const success = Either.right(42);
+const failure = Either.left(500);
+
+const doubled = success.map((x) => x * 2);
+console.log({ doubled: doubled.right });
+
+const result = failure.match(
+  (error) => `Failure: ${error}`,
+  (value) => `Success: ${value}`,
+);
+
+console.log({ result });