Adds FirstOrDefault (#64)

index.d.ts

@@ -12,6 +12,8 @@ interface Array<T> {
   ElementAt<T>(index: number): T;
   First<T>(): T;
   First<T>(predicate: (x: T) => boolean): T;
+  FirstOrDefault<T>(): T;
+  FirstOrDefault<T>(pedicate: (x: T) => boolean): T;
   GroupJoin<T, U, V, K>(
     inner: Array<U>,
     outerKeySelector: ((x: T) => K),

index.js

@@ -4,6 +4,7 @@ const Any = require('./src/Any');
 const Concat = require('./src/Concat');
 const Count = require('./src/Count');
 const ElementAt = require('./src/ElementAt');
+const FirstOrDefault = require('./src/FirstOrDefault');
 const Empty = require('./src/Empty')
 const First = require('./src/First');
 const GroupJoin = require('./src/GroupJoin');
@@ -27,6 +28,7 @@ const bindAll = function() {
   Array.prototype.Concat = Concat;
   Array.prototype.Count = Count;
   Array.prototype.ElementAt = ElementAt;
+  Array.prototype.FirstOrDefault = FirstOrDefault;
   Array.Empty = Empty;
   Array.prototype.First = First;
   Array.prototype.GroupJoin = GroupJoin;

src/FirstOrDefault.js

@@ -0,0 +1,10 @@
+/**
+ * @template T
+ * @param {((x: T) => boolean)} predicate
+ * @returns {T}
+ */
+function FirstOrDefault(predicate) {
+  if (predicate) return this.find(predicate);
+  return this[0];
+}
+module.exports = FirstOrDefault;

test/FirstOrDefault.spec.js

@@ -0,0 +1,24 @@
+const expect = require('chai').expect;
+require('..')();
+
+describe('Array#prototype#First', function() {
+  const input = [2, 4, 6, 8];
+  it('Should return the first value with no predicate passed', function() {
+    const expected = 2;
+    const actual = input.FirstOrDefault();
+    expect(actual).to.eql(expected);
+  });
+  it('Should return the first value matching predicate', function() {
+    const expected = 2;
+    const actual = input.FirstOrDefault(x => x % 2 === 0);
+    expect(actual).to.eql(expected);
+  });
+  it('Should return undefined when no matching element in array with values', function() {
+    const actual = input.FirstOrDefault(x => x === 1);
+    expect(actual).to.be.undefined;
+  });
+  it('Should return undefined when no matching element in empty array', function() {
+    const actual = [].FirstOrDefault();
+    expect(actual).to.be.undefined;
+  });
+});