Encrypting a string based on an algorithm in JavaScript

We are required to write a JavaScript function that takes in a string and encrypts it based on the following algorithm:

• The string contains only space separated words.
• We need to encrypt each word in the string using the following rules:
  • The first letter needs to be converted to its ASCII code.
  • The second letter needs to be switched with the last letter.

Therefore, according to this, the string 'good' will be encrypted as '103doo'.

Algorithm Breakdown

Let's understand how the encryption works with the word 'good':

• First letter 'g' ? ASCII code 103
• Second letter 'o' switches with last letter 'd'
• Middle letters 'o' remain in position
• Result: '103' + 'd' + 'o' + 'o' = '103doo'

Single Word Encryption

const str = 'good';

const encryptString = (str = '') => {
   const [first, second] = str.split('');
   const last = str[str.length - 1];
   let res = '';
   
   // Convert first letter to ASCII
   res += first.charCodeAt(0);
   
   // Add last letter
   res += last;
   
   // Add middle letters (if any)
   for(let i = 2; i < str.length - 1; i++){
      const el = str[i];
      res += el;
   }
   
   // Add second letter at the end
   res += second;
   
   return res;
};

console.log(encryptString(str));

103doo

Multiple Words Encryption

To handle multiple space-separated words, we need to split the string and encrypt each word individually:

const encryptSentence = (sentence = '') => {
   const words = sentence.split(' ');
   const encryptedWords = words.map(word => {
      if (word.length <= 1) return word;
      
      const [first, second] = word.split('');
      const last = word[word.length - 1];
      let res = '';
      
      res += first.charCodeAt(0);
      res += last;
      
      for(let i = 2; i < word.length - 1; i++){
         res += word[i];
      }
      
      res += second;
      return res;
   });
   
   return encryptedWords.join(' ');
};

console.log(encryptSentence('good morning world'));
console.log(encryptSentence('hello javascript'));

103doo 109ornin 119orlo
104ello 106avascrip

Edge Cases Handling

The algorithm should handle edge cases like single-character words and empty strings:

const encryptStringSafe = (str = '') => {
   if (str.length <= 1) return str;
   if (str.length === 2) {
      return str.charCodeAt(0) + str[1];
   }
   
   const [first, second] = str.split('');
   const last = str[str.length - 1];
   let res = '';
   
   res += first.charCodeAt(0);
   res += last;
   
   for(let i = 2; i < str.length - 1; i++){
      res += str[i];
   }
   
   res += second;
   
   return res;
};

console.log(encryptStringSafe('a'));      // Single character
console.log(encryptStringSafe('hi'));     // Two characters
console.log(encryptStringSafe('code'));   // Normal case

a
104i
99odc

Conclusion

This encryption algorithm transforms strings by converting the first character to ASCII and swapping the second and last characters. It's a simple substitution cipher suitable for basic text obfuscation in JavaScript applications.