Added new algoritm

String/MaxCharacter.js

@@ -0,0 +1,29 @@
+/*
+  Given a string of characters, return the character that appears the most often.
+  Example: input = "Hello World!" return "l"
+*/
+const maxCharacter = (value) => {
+  if (typeof value !== 'string') {
+    throw new TypeError('The param should be a string')
+  } else if (!value) {
+    throw new Error('The param should be a valid string')
+  }
+
+  const occurrences = {}
+  for (let i = 0; i < value.length; i++) {
+    const char = value[i]
+    if (/\s/.test(char)) continue
+    occurrences[char] = occurrences[char] + 1 || 1
+  }
+  let maxCharacter = null
+  let maxCount = 0
+  Object.keys(occurrences).forEach(char => {
+    if (occurrences[char] > maxCount) {
+      maxCount = occurrences[char]
+      maxCharacter = char
+    }
+  })
+  return maxCharacter
+}
+
+export { maxCharacter }