add arrayFind (implementation of Array.prototype.find)

src/arrayFind.ts

@@ -0,0 +1,28 @@
+/**
+ * Usage: import arrayFind = require("tsutil/arrayFind");
+ *
+ * arrayFind([1,2,3,4,5], (x) => x === 3);
+ *
+ * @param {Array<T>} list
+ * @param {(x: T) => boolean} predicate
+ * @param {Object} thisArg?
+ * @returns {T?}
+ */
+function arrayFind<T>(
+    list: T[],
+    predicate: (x: T, index: number, list: T[]) => boolean,
+    thisArg?: {}): T {
+
+  var length = list.length;
+  var value: T;
+  for (var i = 0; i < length; i++) {
+    value = list[i];
+    if (predicate.call(thisArg, value, i, list)) {
+       return value;
+    }
+  }
+  return undefined;
+}
+
+export = arrayFind;
+

src/index.ts

@@ -1,6 +1,7 @@
 /**
  * TsUtil Exports
  */
+export import arrayFind = require("./arrayFind");
 export import Handle = require("./handle");
 export import identity = require("./identity");
 export import Optional = require("./optional");

test/arrayFind_spec.ts

@@ -0,0 +1,49 @@
+import chai = require("chai");
+import tsutil = require("../src/index");
+
+var arrayFind = tsutil.arrayFind;
+var assert = chai.assert;
+
+describe("arrayFind", () => {
+
+  var list: number[] = [5, 10, 15, 20];
+
+  it("should find item by predicate", function() {
+    var result = arrayFind(list, (x) => x === 15);
+    assert.equal(result, 15);
+  });
+
+  it("should return undefined when nothing matched", function() {
+    var result = arrayFind(list, (x) => x === -1);
+    assert.equal(result, undefined);
+  });
+
+  it("should receive all three parameters", function() {
+    arrayFind(list, (value, index, arr) => {
+      assert.equal(list[index], value);
+      assert.equal(list, arr);
+      return false;
+    });
+  });
+
+  it("should work with the context argument", function() {
+    var context = {};
+    arrayFind([1], function() {
+      assert.equal(this, context);
+      return false;
+    }, context);
+  });
+
+  it("should work with a sparse array", function() {
+    var obj = [1, , undefined];
+    assert.isFalse(1 in obj);
+    var seen: any[] = [];
+    var found = arrayFind(obj, (x) => {
+      seen.push(x);
+      return false;
+    });
+    assert.equal(found, undefined);
+    assert.sameMembers(seen, [1, undefined, undefined]);
+  });
+});
+