added linear search algorithm

Author: Syed Fasiuddin

src/searching/linearSearch.js

@@ -0,0 +1,24 @@
+(function (exports) {
+    'use strict';
+
+    /**
+     * Searches for specific element in a given array
+     * using the linear search algorithm
+     * Time complexity: O(n)
+     * 
+     * @param {Array} array Input array
+     * @param {Number} key the number whose index is to be found
+     * @returns {Number} the index of the first instance of number or else -1 if not found
+     */
+
+    const linearSearch = (array, key) => {
+        for (let i = 0; i < array.length; i++) {
+            if (array[i] == key) {
+                return i;
+            }
+        }
+        return -1;
+    }
+
+    exports.linearSearch = linearSearch;
+})(typeof window === 'undefined' ? module.exports : window);

test/searching/linearSearch.spec.js

@@ -0,0 +1,28 @@
+var linearSearch =
+  require('../../src/searching/linearSearch').linearSearch;
+
+describe('Linear Search', function () {
+  'use strict';
+
+  it('should find the element at position 0 ', function () {
+    expect(linearSearch([1, 2, 3, 4, 6, 8], 1)).toBe(0);
+  });
+
+  it('should find the element in position arr.length - 1', function () {
+    var arr = [1, 2, 3, 4, 6, 8];
+    expect(linearSearch(arr, 8)).toBe(arr.length - 1);
+  });
+
+  it('should work with arrays with 2 elements', function () {
+    expect(linearSearch([1, 8], 1)).toBe(0);
+    expect(linearSearch([1, 8], 8)).toBe(1);
+  });
+
+  it('should return a negative number for missing elements', function () {
+    expect(linearSearch([1, 2, 3], 4)).toBeLessThan(0);
+  });
+
+  it('should work with empty arrays', function () {
+    expect(linearSearch([], 4)).toBe(-1);
+  });
+});