What is debugging?

JavaScriptJunior~3 min read

Debugging is the process of finding, analyzing, and fixing errors (bugs) in a program. When your code does not work the way you expect, debugging is what helps you understand why that happens and how to fix it.

1. In plain terms

Debugging is when a developer "steps" through the code, watches variables, checks where the program goes wrong, and fixes the cause of the problem.

2. Main goals of debugging

Understand why the code behaves incorrectly.
Find the spot where the error happens.
Fix the bug (a logic, syntax, or data error, and so on).
Verify that everything works correctly after the fix.

3. How debugging happens (step by step)

Discovering the error, the program crashes or behaves differently than expected.
Analysis, you read the error message and study the call stack (stack trace).
Setting breakpoints, to see what happens "inside" the program.
Step-by-step execution, going through the code line by line, checking variable values.
Fixing, finding the source of the error and making changes.
Verification, running it again to confirm the error is truly gone.

4. Debugging tools in JavaScript

Console

The simplest and most popular tool:

javascript

console.log("Variable x:", x);
console.error("Error:", err);
console.table(users);

Used to print intermediate values and understand where things went wrong.

Debugger

A special statement that stops code execution and opens DevTools.

javascript

function test(a, b) {
  debugger; // stops here
  return a + b;
}
test(2, 3);

This opens the browser's developer tools, and you can:

look at variable values,
step through lines,
see the call stack,
control code execution.

Breakpoints

In Chrome DevTools, VS Code, and other IDEs, you can click to the left of a line number, and the program automatically stops there when it runs.

Network / Sources / Call Stack

In the debugger you can:

watch network requests,
look at the source code and variables,
analyze the call stack to understand which function triggered the error.

5. Debugging asynchronous code

In JavaScript it is especially important to be able to debug:

async/await
Promise
timers (setTimeout)
events (click, keydown, and so on)

For this, debuggers support an asynchronous call stack, so you can see the whole path to the error, even if it happened a second after the event.

6. Debugging in practice (example)

javascript

function divide(a, b) {
  if (b === 0) throw new Error("Division by zero!");
  return a / b;
}

function calculate() {
  const x = 10;
  const y = 0;
  const result = divide(x, y);
  console.log("Result:", result);
}

calculate();

Error:

javascript

Uncaught Error: Division by zero!
    at divide (<anonymous>:2:21)
    at calculate (<anonymous>:8:18)

The call stack shows which line and which function triggered the error. That is part of debugging too.

7. Debugging in Node.js

Node.js also supports debugging. You can start the program with a flag:

javascript

node --inspect index.js

Then open Chrome at chrome://inspect, to see breakpoints and the stack right in the browser.

8. Debugging tools

Tool	Where it is used
Chrome DevTools	Debugging the frontend, network requests, the DOM
VS Code Debugger	Step-by-step debugging of Node.js and browser JS
Sentry / GlitchTip	Tracking errors in production
console.log / debugger	Quick manual checks

Summary

Term	Description
Debugging	The process of finding and fixing errors
debugger	A keyword that pauses the code
breakpoint	A point where code execution stops
stack trace	The path of function calls leading to the error
console.log()	A quick way to see data
DevTools / VS Code Debugger	The main tools for debugging JS

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