Chapter 1: Understanding Software Bugs

Software bugs represent unexpected or incorrect behaviors within applications, including web apps. The presence of a bug can significantly diminish the quality of a web app, depending on its severity. Critical bugs can disrupt the entire application, affecting user interaction, while minor bugs may only impact specific user flows, often manageable through alternative pathways. The established debugging process allows developers to identify and eliminate these bugs, restoring the application's quality.

Modern web browsers, equipped with comprehensive development environments, offer robust debugging tools to identify issues in JavaScript code. Google Chrome, for instance, provides the DevTools panel, which is essential for effective JavaScript debugging. This tool not only features standard breakpoint-based dynamic analysis but also advanced functionalities such as variable watchers and stack frame inspectors. Additionally, DevTools supports debugging for TypeScript, Node.js, Deno, and React Native applications through its protocol. Most frontend frameworks also provide DevTools extensions to enhance the debugging experience, such as the React Developer Tools.

Understanding the productivity-enhancing features of Chrome DevTools can significantly accelerate your JavaScript debugging process, enabling you to implement bug fixes more efficiently. This article will explore the various DevTools features that can enhance your debugging productivity. By mastering these tools, you can concentrate on debugging rather than getting bogged down by the process.

The first video, "Chrome Debugger is BETTER than you might think," delves into the capabilities of the Chrome Debugger and how it can enhance your debugging experience.

Section 1.1: Watching Variables and Expressions

When the debugger hits a breakpoint, you can inspect JavaScript variables by hovering over them. While this allows you to view atomic values and objects during debugging, it can become cumbersome if you need to monitor multiple variables simultaneously. This task is further complicated if you need to evaluate expressions involving these variables, as it requires frequent switching between the debugger and console.

DevTools enables you to track variables and expressions based on breakpoints or refresh them manually without halting execution. Consider the following code snippet:

let m = 0;

let s = 0;

setInterval(() => {

s++;

if(s === 60) {

m++;

s = 0;

}

}, 1000);

This code sets up a simple timer with two variables. You can monitor the variables m and s by adding watchers and setting breakpoints:

By removing the breakpoint, you can refresh the view instead, allowing you to evaluate expressions dynamically. For instance, you can print timer values with leading zeros.

Subsection 1.1.1: Utilizing the Debugger Context in the Console

You can examine object properties by hovering over them and setting watchers. However, in certain scenarios, you may need to invoke object methods and inspect properties with auto-complete support in the console. DevTools allows you to adjust the console's scope to the current breakpoint. For example, to check the return value of the getMilliseconds() method for a date object:

function getMagicDate(d) {

if(d.getDate() % 2 === 0) {

d.setDate(d.getDate() + 2);

} else {

d.setMonth(d.getMonth() + 1);

}

return d;

}

getMagicDate(new Date());

Set a breakpoint, halt the execution, and open the console drawer to execute the necessary method:

Section 1.2: Creating Live Expressions Without Breakpoints

In previous examples, we utilized watchers to inspect variables, requiring us to halt at breakpoints or refresh to see updated results. DevTools allows for the creation of live expressions in the console, enabling you to see real-time updates without stopping execution.

Utilizing the earlier timer code:

let m = 0;

let s = 0;

setInterval(() => {

s++;

if(s === 60) {

m++;

s = 0;

}

}, 1000);

You can create live expressions for m and s to observe their values in real-time:

Try creating a live expression to display the timer's value in mm:ss format.

Chapter 2: Accessing Console Results

If you're familiar with Bash scripting, you understand how to retrieve the exit code of the last completed process using the $? variable. Similarly, DevTools offers features that enhance debugging productivity. When evaluating multiple expressions in the console, you can use the predefined $_ variable to access the result of the last expression, which is particularly useful during debugging.

For example:

Additionally, the $0 variable allows you to reference the selected DOM element from the DevTools inspector:

Refer to the official Chrome console utility documentation for more shorthand variables and functions available during JavaScript debugging.

The second video, "Redefining a function as you debug it in Chrome DevTools," showcases the LiveEdit feature in action, allowing for dynamic function updates while debugging.

Chapter 3: Event Listener Breakpoints

Web browsers provide developers with various events to create high-quality, user-friendly applications. Developers typically use event listener callbacks in their JavaScript code. While setting breakpoints for known callbacks is straightforward, debugging unfamiliar code with numerous event listeners can be challenging.

DevTools simplifies this by allowing breakpoints to be set based on event names. For instance:

let btn = document.getElementById('btn');

let count = 0;

btn.addEventListener('click', (e) => {

btn.innerText = Clicked ${++count} times;

});

You can set a breakpoint for this event listener easily, but in a complex codebase, DevTools lets you set breakpoints for various event types:

Chapter 4: Network Request Breakpoints

This method enables you to pinpoint the exact line of code that triggered a specific network request, streamlining the debugging process.

Chapter 5: Inspecting the Call Stack

To improve code clarity, developers often decompose their source code into multiple functions and organize them into modules. Consequently, when a user triggers an action within a web app, various JavaScript functions execute, creating a call stack in the JavaScript engine. Analyzing stack frames is crucial for debugging recursive functions and understanding function call hierarchies.

Using the stack frame analyzer is straightforward; employing the debugger keyword opens the call stack, allowing you to inspect each stack frame's scope:

Understanding stack structures and their application in programming will enhance your skills as a developer.

Thank you for reading!