Debug JavaScript in Production With Source Maps

These days, the code you use to write your application isn’t usually the same code that’s deployed in production and interpreted by browsers. Perhaps you’re writing your source code in a language that “compiles” to JavaScript, like CoffeeScript, TypeScript, or the latest standards-body approved version of JavaScript, ECMAScript 2015 (ES6). Or, even more likely, you’re minifying your source code in order to reduce the file size of your deployed scripts. You’re probably using a tool like UglifyJS or Google Closure Compiler.
Such transformation tools are often referred to as transpilers — tools that transform source code from one language into either the same language or another similar high-level language. Their output is transpiled code that, while functional in the target environment (e.g., browser-compatible JavaScript), typically bears little resemblance to the code from which it was generated.