merge: Upgrade Lower function (TheAlgorithms#894)

* docs: update the js doc

* pref: Optimize algo via regex

ignore the useless traverse in best case via regex and String.prototype.replace

* test: add some new test cases

* fix: styled with standard

* refactor: remove useless variable

Author: fahimfaisaal

String/Lower.js

@@ -1,8 +1,8 @@
 /**
  * @function lower
  * @description Will convert the entire string to lowercase letters.
- * @param {String} url - The input URL string
- * @return {String} Lowercase string
+ * @param {String} str - The input string
+ * @returns {String} Lowercase string
  * @example lower("HELLO") => hello
  * @example lower("He_llo") => he_llo
  */
@@ -12,17 +12,12 @@ const lower = (str) => {
     throw new TypeError('Invalid Input Type')
   }
 
-  let lowerString = ''
+  return str
+    .replace(/[A-Z]/g, (_, indexOfUpperChar) => {
+      const asciiCode = str.charCodeAt(indexOfUpperChar)
 
-  for (const char of str) {
-    let asciiCode = char.charCodeAt(0)
-    if (asciiCode >= 65 && asciiCode <= 90) {
-      asciiCode += 32
-    }
-    lowerString += String.fromCharCode(asciiCode)
-  }
-
-  return lowerString
+      return String.fromCharCode(asciiCode + 32)
+    })
 }
 
 export { lower }

String/test/Lower.test.js

@@ -1,9 +1,19 @@
 import { lower } from '../Lower'
 
-describe('Lower', () => {
-  it('return uppercase strings', () => {
-    expect(lower('hello')).toBe('hello')
+describe('Testing the Lower function', () => {
+  it('Test 1: Check by invalid type', () => {
+    expect(() => lower(345)).toThrowError()
+    expect(() => lower(true)).toThrowError()
+    expect(() => lower(null)).toThrowError()
+  })
+
+  it('Test 2: Check by uppercase string', () => {
     expect(lower('WORLD')).toBe('world')
-    expect(lower('hello_WORLD')).toBe('hello_world')
+    expect(lower('Hello_WORLD')).toBe('hello_world')
+  })
+
+  it('Test 3: Check by lowercase string', () => {
+    expect(lower('hello')).toBe('hello')
+    expect(lower('hello_world')).toBe('hello_world')
   })
 })