feat: Add startsWith function (#50)

Closes #49

Author: Chikel

src/index.js

@@ -11,6 +11,7 @@ import isArray from './is-array'
 import validateEmail from './validateEmail'
 import hex2rgb from './hex2rgb'
 import isNullOrWhitespace from './is-null-or-whitespace'
+import startsWith from './startsWith'
 
 export {
   flatten,
@@ -26,4 +27,5 @@ export {
   validateEmail,
   hex2rgb,
   isNullOrWhitespace,
+  startsWith,
 }

src/startsWith.js

@@ -0,0 +1,16 @@
+export default startsWith
+
+/**
+ * Original Source: http://stackoverflow.com/a/646631/5954939
+ *
+ * This method will return a bollean indicating whether a string starts with a given input.
+ *
+ * @param {String} str - The string to validate against
+ * @param {String} head - The input to match with str substring
+ * @return {Bollean} - True if 'str' starts with 'head', otherwise false
+ */
+function startsWith(str, head) {
+  const tmp = str.substring(0, head.length)
+  const res = (tmp === head)
+  return res
+}

test/startsWith.test.js

@@ -0,0 +1,16 @@
+import test from 'ava'
+import {startsWith} from '../src'
+
+test('check correct input', t => {
+  const string = 'First PR'
+  const head = 'Fir'
+  const result = startsWith(string, head)
+  t.true(result)
+})
+
+test('check wrong input', t => {
+  const string = 'First PR'
+  const head = 'Foo'
+  const result = startsWith(string, head)
+  t.false(result)
+})