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Debugging in JavaScript is the process of finding and fixing errors in your code to make it run correctly. It helps identify issues like syntax errors, logic mistakes, or unexpected behavior. JavaScript provides built-in tools such as the console (for logging messages) and the debugger statement (to pause and inspect code). Using browser Developer Tools, you can check variables, set breakpoints, and step through code for smooth and error-free performance.
Debugging is the process of finding, understanding, and fixing errors (bugs) in your code. In JavaScript, these bugs can be:
The goal of debugging is not only to fix errors but also to understand why they occurred to prevent them in the future.
console ObjectThe console object provides several helpful methods to print messages, debug values, and inspect program flow in your browser’s console (available via DevTools).
console Methodsconsole.log()
Used to display general information and variable values.
const name = "Alice";
console.log("User name is:", name);
console.error()
Displays an error message in red text, useful for reporting problems.
console.error("Something went wrong!");
console.warn()
Shows a warning message (yellow text), often used for potential issues.
console.warn("Deprecated method detected!");
console.table()
Displays array or object data in a table format for better readability.
const users = [
{ name: "John", age: 25 },
{ name: "Sara", age: 30 }
];
console.table(users);
console.group() and console.groupEnd()
Organizes console output into collapsible groups.
console.group("User Info");
console.log("Name: Alice");
console.log("Age: 22");
console.groupEnd();
console.time() and console.timeEnd()
Measures execution time for performance testing.
console.time("Loop time");
for (let i = 0; i < 1000000; i++) {}
console.timeEnd("Loop time");
debugger StatementThe debugger keyword is a built-in JavaScript statement that pauses code execution at a specific point, allowing you to inspect variables, step through code, and analyze logic in browser DevTools.
function calculate(a, b) {
debugger; // Code execution stops here
return a + b;
}
calculate(5, 10);
Modern browsers (like Chrome, Edge, and Firefox) have powerful developer tools built in.
To open:
Ctrl + Shift + I or F12Cmd + Option + IYou can click the line number in the “Sources” tab to set breakpoints, which pause execution automatically at that line.
Tools like ESLint and Prettier help detect potential bugs and maintain code consistency.
Example configuration (for ESLint):
npm install eslint --save-dev
npx eslint yourfile.js
Breakpoints let you pause code at a certain line without changing the source code (unlike the debugger keyword).
Once paused, you can:
This feature is especially useful in complex apps or loops to monitor variable changes.