[Feature] Upgrade project's JavaScript code with the power of ES6! for better performance.

## Problem
Using these concepts can lead to more concise and readable code, with fewer bugs and better performance. Additionally, many of these concepts are supported by modern browsers and Node.js versions, making it easier to write code that can be run in multiple environments.

## Description
There are several ways to improve the implementation, such as replacing all instances of var with const or let, implementing arrow functions, and ensuring that each function handles edge cases.

For eg:-

The function "getUrlVars()" declared in the "listing.html" file uses the "var" keyword for variable declaration, which may lead to variable scoping issues. Additionally, the code doesn't account for URL encoding of parameter values, which may cause incorrect capture of special characters. Moreover, the variable names used in the function are not very descriptive, which could make the code harder to comprehend and update.

## Implementation

- [X] I would be interested in implementing this feature.