rplansky
diff --git a/‎__tests__/Seq.ts
Lines changed: 16 additions & 0 deletions b/‎__tests__/Seq.ts
Lines changed: 16 additions & 0 deletions
diff --git a/‎src/CollectionImpl.js
Lines changed: 8 additions & 8 deletions b/‎src/CollectionImpl.js
Lines changed: 8 additions & 8 deletions
diff --git a/‎type-definitions/Immutable.d.ts
Lines changed: 10 additions & 5 deletions b/‎type-definitions/Immutable.d.ts
Lines changed: 10 additions & 5 deletions
diff --git a/‎type-definitions/immutable.js.flow
Lines changed: 2 additions & 2 deletions b/‎type-definitions/immutable.js.flow
Lines changed: 2 additions & 2 deletions
@@ -10,6 +10,22 @@
 import { isCollection, isIndexed, Seq } from '../';
 
 describe('Seq', () => {
+  it('returns undefined if empty and first is called without default argument', () => {
+    expect(Seq().first()).toBeUndefined();
+  });
+
+  it('returns undefined if empty and last is called without default argument', () => {
+    expect(Seq().last()).toBeUndefined();
+  });
+
+  it('returns default value if empty and first is called with default argument', () => {
+    expect(Seq().first({})).toEqual({});
+  });
+
+  it('returns default value if empty and last is called with default argument', () => {
+    expect(Seq().last({})).toEqual({});
+  });
+
   it('can be empty', () => {
     expect(Seq().size).toBe(0);
   });
 
@@ -371,8 +371,8 @@ mixin(Collection, {
       .findKey(predicate, context);
   },
 
-  first() {
-    return this.find(returnTrue);
+  first(notSetValue) {
+    return this.find(returnTrue, null, notSetValue);
   },
 
   flatMap(mapper, context) {
@@ -423,10 +423,10 @@ mixin(Collection, {
       .toIndexedSeq();
   },
 
-  last() {
+  last(notSetValue) {
     return this.toSeq()
       .reverse()
-      .first();
+      .first(notSetValue);
   },
 
   lastKeyOf(searchValue) {
@@ -627,8 +627,8 @@ mixin(IndexedCollection, {
     return entry ? entry[0] : -1;
   },
 
-  first() {
-    return this.get(0);
+  first(notSetValue) {
+    return this.get(0, notSetValue);
   },
 
   flatten(depth) {
@@ -671,8 +671,8 @@ mixin(IndexedCollection, {
     return Range(0, this.size);
   },
 
-  last() {
-    return this.get(-1);
+  last(notSetValue) {
+    return this.get(-1, notSetValue);
   },
 
   skipWhile(predicate, context) {
 
@@ -3810,15 +3810,20 @@ declare module Immutable {
     contains(value: V): boolean;
 
     /**
-     * The first value in the Collection.
+     * In case the `Collection` is not empty returns the first element of the
+     * `Collection`.
+     * In case the `Collection` is empty returns the optional default
+     * value if provided, if no default value is provided returns undefined.
      */
-    first(): V | undefined;
+    first<NSV>(notSetValue?: NSV): V | NSV;
 
     /**
-     * The last value in the Collection.
+     * In case the `Collection` is not empty returns the last element of the
+     * `Collection`.
+     * In case the `Collection` is empty returns the optional default
+     * value if provided, if no default value is provided returns undefined.
      */
-    last(): V | undefined;
-
+    last<NSV>(notSetValue?: NSV): V | NSV;
 
     // Reading deep values
 
 
@@ -63,8 +63,8 @@ declare class _Collection<K, +V> /*implements ValueObject*/ {
   has(key: K): boolean;
   includes(value: V): boolean;
   contains(value: V): boolean;
-  first(): V | void;
-  last(): V | void;
+  first<NSV>(notSetValue?: NSV): V | NSV;
+  last<NSV>(notSetValue?: NSV): V | NSV;
 
   hasIn(keyPath: Iterable<mixed>): boolean;