Smart concatenation of strings in JavaScript

We are required to write a JavaScript function that takes in two strings and concatenates the second string to the first string.

If the last character of the first string and the first character of the second string are the same then we have to omit one of those characters.

Example

The code for this will be −

const str1 = 'Food';
const str2 = 'dog';
const concatenateStrings = (str1, str2) => {
   const { length: l1 } = str1;
   const { length: l2 } = str2;
   if(str1[l1 - 1] !== str2[0]){
      return str1 + str2;
   };
   const newStr = str2.substr(1, l2 - 1);
   return str1 + newStr;
};
console.log(concatenateStrings(str1, str2));

Output

The output in the console −

Foodog