Encrypting a String Using Caesar Cipher in JavaScript

Caesar Cipher Algorithm

The Caesar Cipher algorithm is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet.

For example

With a left shift of 3, D would be replaced by A, E would become B, and so on. We are required to write a JavaScript function that takes in a string to be encrypted as the first argument and a shift amount as the second argument.

The shift amount can be a positive or negative integer (a positive shift signifies a shift to right whereas negative to left).

Example

Following is the code −

const str = 'thisIsAString';
const getMap = (legend, shift) => {
   return legend.reduce((charsMap, currentChar, charIndex) => {
      const copy = { ...charsMap };
      let ind = (charIndex + shift) % legend.length;
      if (ind < 0) {
         ind += legend.length;
      };
      copy[currentChar] = legend[ind];
      return copy;
   }, {});
};
const encrypt = (str, shift = 0) => {
   const legend = 'abcdefghijklmnopqrstuvwxyz'.split('');
   const map = getMap(legend, shift);
   return str
   .toLowerCase()
   .split('')
   .map(char => map[char] || char)
   .join('');
};
console.log(encrypt(str, 6));

Output

Following is the output on console −

znoyoygyzxotm