JavaScript Debugging

Importance of Debugging Skills

“The most frustrating part about coding is trying to find and fix bugs in your code.”

• Debugging is an essential skill that many developers overlook, regardless of their experience level.
• Understanding how to debug effectively helps to minimize the time spent identifying issues, allowing more time for writing code, which is generally more enjoyable.

Getting Started with Debugging

“The first important thing to understand is how you can actually use the tools provided to debug issues in your code.”

• Beginners should familiarize themselves with the debugging tools available to them for solving problems that arise in their code.
• For instance, when debugging a code snippet that involves functions, recognizing the error messages provided, such as an “uncaught reference error,” is crucial for diagnosing the problem.

Analyzing Error Messages

“The most important thing to look at anytime you get an error message is where that error message occurred.”

• The top line of the error message gives crucial information about what went wrong, including the type of error and specifics on the location in the code where the problem occurred.
• Each error message typically shows the specific line number, enabling the developer to quickly identify where to focus their debugging efforts.

Using Console Logs for Basic Debugging

“Throwing in a couple console log statements to see what’s going on with your variables is really important.”

• If an error isn’t explicitly shown as a message, using console logs allows developers to trace the execution flow of their code and check the state of variables.
• By strategically placing console logs in code, developers can verify whether certain code branches are being executed and what values variables hold at various points in time.

Transitioning to a Debugger Tool

“To start using an actual proper debugger, you can just type in the word ‘debugger’ anywhere inside your code.”

• Once console logs become cumbersome, utilizing the built-in debugger tool makes complex debugging tasks easier.
• In browsers like Chrome, typing “debugger” will pause execution, allowing developers to inspect the current state of their code and variables much more efficiently.

Debugging JavaScript with Breakpoints

“This code execution is paused at the debugger line, allowing me to inspect variable values.”

• The debugger feature in JavaScript provides the capability to pause code execution at specified lines, enabling developers to examine variable values at that moment.
• When the execution is paused, developers can hover over variables to view their current values, which aids in understanding the program’s state.
• Resuming execution unpauses the code until the next breakpoint or until the program completes, allowing developers to step through their code effectively without interruptions.

Using Step Buttons for Code Navigation

“The step function behaves similarly to step into but is designed for asynchronous code.”

• Multiple step functions offer different ways to navigate through code during debugging.
• The “Step Into” function allows developers to enter the code of a called function, pausing execution at the first line of that function, which enables detailed inspection of nested calls.
• The “Step Over” function bypasses the function call and pauses at the next line of code, making it useful when depth navigation isn’t necessary.
• The “Step Out” function quickly exits the current function and proceeds to the next line after the function call, minimizing unnecessary stepping through every line within the function.

Handling Asynchronous Code

“When using ‘Step Into’ on asynchronous functions like setTimeout, the debugger will wait before proceeding.”

• The introduction of asynchronous code modifies how traditional debugging functions operate, with special attention needed for functions like setTimeout.
• When a developer uses the “Step Into” function on an asynchronous call, such as setTimeout, the debugger will pause execution until after the asynchronous operation completes, allowing for inspection only once it has run.

Utilizing Breakpoints for Error Tracking

“By enabling ‘pause on uncaught exceptions,’ the debugger will stop execution at the error’s location.”

• Setting a breakpoint to pause on uncaught exceptions is a powerful way to identify where errors occur in the code, as it allows the debugger to halt execution right where an error arises.
• This feature helps developers trace back to the problematic line and understand the context of the error, making debugging more efficient.
• The call stack section displays the current functions being executed and their order, enabling easy navigation back through the code’s path to identify the source of errors.

Understanding the Call Stack

“Being able to go through the call stack level by level is really great.”

• The call stack allows developers to track the sequence of function calls made in the code, which helps in understanding how the program reached a specific state or encountered an error.
• As functions are called, they are added to the stack, and their scope and associated variables are maintained at each level.
• This visibility into the call stack can make it easier to debug issues, as developers can clearly see the path that execution has taken and what variables are in scope.

Utilizing Breakpoints in Debugging

“Anywhere in your code, you can add a breakpoint.”

• Breakpoints are markers that can be set in code to pause execution at specified lines. This allows developers to inspect current states without modifying the source code directly.
• In the Chrome debugger, you can create a breakpoint by clicking the line number where you want to stop execution, allowing for targeted troubleshooting even in production environments.
• Breakpoints can easily be managed by disabling or removing them, making debugging more efficient.

Fetch and Event Listener Breakpoints

“This is a great way to add a breakpoint any time I make a fetch statement.”

• Fetch breakpoints trigger whenever a fetch request is made to a specified URL, allowing developers to closely examine network interactions without knowing all the code details.
• Additionally, event listener breakpoints can be established to pause execution whenever specific events, like mouse clicks, occur, granting insights into user interactions and their effects on the web application.

Working with DOM Breakpoints

“We can actually do a breakpoint on these different things, which is great.”

• DOM breakpoints allow developers to monitor changes to elements on the web page. They can be configured for various types of modifications, such as attribute changes, node removals, or subtree modifications.
• For example, when an element is removed or its attributes are modified, execution can pause, letting developers inspect the context of the change, which is particularly beneficial for debugging dynamic content.

Exploring Global Listeners and CSP Breakpoints

“These are essentially listeners that are set up on the window object.”

• Global listeners capture events that occur on a broader scale, such as within the window object. These are useful for debugging events that may not be confined to a specific element.
• CSP (Content Security Policy) breakpoints help detect violations in large applications with security policies set up, allowing developers to monitor and manage security-related errors effectively.

Utilizing the Watch Tab

“You can see that essentially it’s going to give me the value of the first name variable anywhere inside of my code.”

• The Watch tab in the debugger tool allows developers to track the value of specific variables throughout code execution, providing updated information as the code runs.
• This feature can be particularly useful for monitoring variables that change frequently, as it helps maintain awareness of their state at various points in the application flow.

Debugging with Chrome and Visual Studio Code

“This watch section… is really useful if you want to track a variable through an entire set of code.”

• The watch section in Chrome’s debugger allows users to monitor specific variable values throughout the execution of code. This is especially helpful in larger functions where variables may change frequently.
• Users can also track expressions involving multiple variables, such as combining a first name and last name, allowing for a clearer understanding of their code’s behavior.
• Although useful, many developers prefer the scoping section for obtaining similar information more directly.
• The video discusses how to use the Chrome debugger effectively, highlighting that it provides tools like the watch section and the scoping section, but that many prefer Visual Studio Code for a more streamlined debugging experience.

Setting Up Debugging in Visual Studio Code

“The first thing we need to do is go to this tab right here called run and debug.”

• To begin debugging in Visual Studio Code, users should navigate to the “Run and Debug” tab, usually found at the bottom of the interface.
• Depending on their project type, developers can select the appropriate debugging option, such as “Web App in Chrome” for web applications or “Node.js” for server-side applications.
• Users will need to provide the URL where their application is running, typically in the format of localhost on the specific port designated by their live server setup.
• For instance, if using a live server extension, users might set the URL to localhost:5500.

Debugging Features in Visual Studio Code

“At the top, I have this little bar that I can use to pause, step over, step into, step out of, all those same things that we’re used to.”

• Visual Studio Code has a debugging toolbar that provides options to pause execution, step over, step into, or step out of functions, closely mimicking the features offered in Chrome’s debugger.
• Adding a debugger statement in the code will trigger a pause in execution, allowing developers to inspect the state of their application when the code reaches that point.
• The debugging console, available within Visual Studio Code, allows users to view output and variables directly without needing to transition to another interface, thus enhancing the debugging experience.

Advanced Debugging Techniques

“I can also put in slightly more customized breakpoints… like a conditional breakpoint.”

• In Visual Studio Code, users can create various types of breakpoints, including conditional breakpoints that only trigger execution halts when certain conditions are met.
• These advanced options allow for more precise control during debugging and can significantly streamline the process for developers dealing with complex code bases.
• Log points can also be implemented, offering a way to log variable values during execution without adding console logging statements directly in the code.
• Triggered breakpoints provide another layer of control, allowing execution to pause based on specific criteria set by the developer.

Using Breakpoints Efficiently

“Understanding how to set and manage breakpoints can greatly enhance debugging efficiency.”

• The tutorial demonstrates how to set breakpoints in code to pause execution at specified lines. Initially, breakpoints are placed to test their functionality, confirming they can be triggered correctly during code execution.
• After confirming the breakpoints work, they are removed to revert the code to its previous state. A new breakpoint is then introduced with a condition that the variable n must be greater than 30 for the execution to pause. This conditional breakpoint illustrates that if the condition is not met, the corresponding code block will never execute.
• The significance of conditional breakpoints becomes clear; they allow developers to pause execution only when specific conditions are met, helping to focus on relevant scenarios during debugging.

Debugging Fetch Requests in VS Code

“Setting fetch breakpoints allows for targeted debugging of network requests.”

• In this segment, the focus shifts to setting fetch breakpoints in VS Code, which are useful for monitoring network requests made by the application. By using a command, developers can specify a URL for which they want to trigger a fetch breakpoint.
• This functionality enables the developer to pause execution whenever a fetch request is made to the specified URL, thus providing deeper insights into network activity within larger projects.

Understanding the Network Tab in Chrome DevTools

“The network tab is essential for analyzing all network requests made by your application.”

• The network tab in Chrome DevTools provides a clear view of all resources fetched by the webpage. It offers a comprehensive list of requests, such as HTML, CSS, JavaScript, and images, that are crucial for debugging.
• Developers are encouraged to refresh the page within the network tab to capture all outgoing requests, which allows for efficient monitoring of resource loads and response times.
• The user can filter requests for specific types, such as only fetch requests or by file type (e.g., documents, images), to simplify the debugging process, especially when dealing with complex applications.

Leveraging Performance Monitoring Tools

“Performance tabs can unveil bottlenecks in your application.”

• The performance tab is introduced as a tool for profiling an application’s performance by recording specific actions and analyzing their execution times. This is especially useful to identify any slow processes and how they affect overall application performance.
• Users can also explore other tabs such as application storage to manage cookies and other stored data, as well as utilize the Lighthouse tab to assess performance metrics, accessibility, and best practices for web applications.

Diagnosing Website Performance Issues

“This is a really great way to see what the different problems inside of your site are.”

• Identifying performance issues on your website is essential for improving user experience. Tools that analyze your site can pinpoint problems like slow-loading images and other elements that may degrade performance.
• For example, a diagnostic tool may indicate that certain images take a long time to load, which affects the overall speed of your page. Understanding these specific issues allows you to take targeted action to fix them.

Scoring and Feedback on Content Quality

“If your page had more information, it would give you a score between 0 and 100 telling you how good you were at these things.”

• When evaluating a webpage, certain tools can offer a score that ranges from 0 to 100. This score reflects how well your page performs based on various criteria, particularly when dealing with content volume and quality.
• In situations where a page is sparse or contains minimal information, such tools may indicate the lack of content as a problem. More robust pages are likely to receive higher scores, highlighting the importance of comprehensive content creation.

Debugging Guidance and Next Steps

“It’s going to give you a bunch of different warnings and errors down here for the exact things you’re missing inside of it that you can fix.”

• Utilizing performance diagnostic tools provides detailed warnings and errors related to the shortcomings of your page. Understanding these specifics allows webmasters and developers to address and rectify issues effectively.
• The insights gained from such tools are fundamental for debugging and improving site quality. They can guide users on what adjustments to make to enhance overall site functionality and performance.

Ref: Web Dev Simplified - YouTube