How I Find Hidden Vulnerabilities Inside JavaScript Files: Step-by-Step Bug Bounty Guide

A simple, practical method to dig secrets, endpoints, and bugs out of JS files — with every command you need

Whenever we do bug bounty on a target most of us only look at the main website — login page, forms, APIs. But one goldmine that a lot of people miss is JavaScript files.

JS files often have things developers accidentally left behind:

• API keys and tokens
• Hidden/internal endpoints
• Admin panel URLs
• Subdomain names
• Database credentials
• Debug/test routes

In this article, I’ll walk you through the exact process from recon to exploitation that I personally use on my own targets.

Step 1: Collect all the JS files of the target

First, we need to build a list of all the JS files on the target. For this, we use a few tools.

Tool 1 — waybackurls (fetches old and current JS files):

waybackurls target.com | grep "\.js$" > js_files.txt