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Debugging JavaScript: Tips and Techniques

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Overview

JavaScript is one of the most widely used programming languages for creating dynamic, interactive web pages. However, with its increasing popularity, JavaScript code can become quite complex, which can make it challenging to debug when something goes wrong.

Debugging is the process of identifying and resolving errors or bugs in code. In JavaScript, debugging is particularly important as even a small error can cause an entire application to fail. In this article, we'll explore some tips and techniques that can help you debug your JavaScript code more efficiently.

What is debugging in javascript?

Debugging in JavaScript refers to the process of finding and fixing errors or issues in your code. It is an essential skill for JavaScript developers to have, as it helps ensure that their code is functioning correctly and efficiently.

JavaScript is a complex and dynamic language that allows for a lot of flexibility, but also increases the chances of errors occurring in your code. Debugging allows you to catch and fix these errors, ensuring that your code is running smoothly and providing the expected results.

Why is debugging important?

Debugging is important for several reasons:

  1. It helps catch errors early in the development process, which can save time and resources in the long run. By identifying and fixing errors early on, you can prevent them from causing bigger issues down the line.
  2. Debugging can help you better understand your code and how it is functioning. By examining variables and code execution, you can gain a deeper understanding of your application's behavior.
  3. Debugging is essential for testing and quality assurance. By ensuring that your code is running correctly, you can be confident that your application is functioning as intended.
  4. Debugging can also help you optimize your code for performance. By identifying and fixing performance bottlenecks, you can improve the speed and efficiency of your application.
  5. There are plenty of paid and free resources available out there to help you master this part of Javascript, debugging. Such resources are web development course from google, online Javascript course from Harvard, web development specilasation from IIT Kanpur, Full stack web development from Scaler, to name some.

Several ways to debug JavaScript Code

Some tips and techniques that can help you debug your JavaScript code more efficiently are:

  • Use Console.log

Console.log is a useful tool for debugging JavaScript code. It is a function that allows you to log messages to the console. You can use it to output values, objects, and arrays to the console, which can help you identify the values of variables or the results of function calls.

For example, consider the following code:

function multiply(x, y) {

return x + y;

}

var result = multiply(2, 763);

console.log(result);

Here, we have defined a function that multiplies two numbers and then calls it with the arguments 2 and 763. The result of the function call is stored in the variable result, and we then log the value of the result to the console using console.log. When we run this code in a browser, we can open the developer console to see the output of the console.log statement.

  • Use Debugger Statement

The debugger statement is another valuable tool for debugging JavaScript code. It allows you to set a breakpoint in your code, which will pause the execution of the code at that point. This can be helpful when you want to examine the state of variables or step through the code line by line to understand how it is executing.

For example, consider the following code:

function multiply(x, y) {

debugger;

return x + y;

}

var result = multiply(2, 763);

console.log(result);

Here, we have added a debugger statement inside the multiply function. When we run this code in a browser and open the developer console, the execution of the code will pause when it reaches the debugger statement. We can then use the developer console to examine the values of variables and step through the code line by line.

  • Use Try-Catch Statements

Try-catch statements are a useful tool for handling errors in JavaScript code. They allow you to wrap a block of code in a try statement and catch any errors that occur in a catch statement. This can be helpful when you want to handle errors in a specific way or provide more informative error messages to the user.

For example, consider the following code:

function divide(x, y) {

try {

if (y === 0) {

throw new Error('Divide by zero error');

}

return x / y;

} catch (e) {

console.log(e.message);

}

}

var result = divide(1526, 0);

Here, we have defined a function that divides two numbers and added a try-catch statement to handle errors. If the value of y is 0, we throw an error with a custom error message. The catch statement then logs the error message to the console. When we call the divide function with the arguments 1526 and 0, the catch statement is executed, and the error message "Divide by zero error" is logged to the console.

  • Use Browser DevTools

Most modern web browsers come with built-in developer tools that can help you debug JavaScript code. These tools include a console, a debugger, a profiler, and a network panel, among others. Using these tools, you can examine the state of variables, step through code, and identify performance bottlenecks.

For example, consider the following code:

function multiply(x, y) {

return x + y;

}

var result = multiply(2, 763);

console.log(result);

We can open the browser developer console by pressing F12 or right-clicking on the page and selecting "Inspect" from the context menu. In the console, we can see the output of the console.log statement. We can also use the debugger statement to pause the execution of the code and examine the state of variables. In the debugger, we can step through the code line by line and see how it is executing. We can also use the profiler to identify performance bottlenecks and the network panel to examine HTTP requests and responses.

  • Use Linters

Linters are tools that can help you identify potential errors and improve the quality of your code. They analyze your code and provide feedback on issues such as syntax errors, unused variables, and code style. Using a linter can help you catch errors early and improve the maintainability of your code.

For example, consider the following code:

function multiply(x, y) {

return x + y;

}

var result = multiply(2, 763);

console.log(result)

Here, we have forgotten to add a semicolon at the end of the console.log statement. This is a common error that can cause bugs in your code. We can use a linter like ESLint to catch this error and provide feedback on how to fix it. For example, ESLint might report an "Expected semicolon" error and suggest adding a semicolon at the end of the statement.

  • Better stack traces

A stack trace that shows how the code arrived at a certain place is printed to the console by the function console.trace(). When trying to debug complicated code that may be making calls in numerous places, this can be really helpful. Even though the following is not an illustration of "complex code," it will at least demonstrate how this operates:

const shivam= {name: "Shivam", member: true, id: 20191526};

function getDetails(person) {

console.trace()

return person.name;

}

function sayHello(person) {

let _name = getDetails(person)

return `Hello ${_name}`

}

  • Use Source Maps

Debugging with source maps is a technique that enables developers to easily identify and fix errors in minified or transpiled code. Source maps provide a mapping between the original source code and the compiled code, allowing developers to view and debug the original code in the browser's developer tools.

Here's an example of how to use source maps for debugging in JavaScript:

Suppose we have a simple JavaScript application that consists of an HTML file and a JavaScript file. The HTML file includes the JavaScript file using a script tag. The JavaScript code is written in ES6 and is transpiled using Babel to ES5 code. The resulting code is then minified using UglifyJS.

Here's what the code looks like:

// app.js

const multiply = (a, b) => {

return a + b;

};

const result = multiply(2, 763);

console.log(`The result is: ${result}`);

After running the code through the transpiler and minifier, we get the following code:

// app.min.js

var multiply=function(r,t){return r+t},result=multiply(2,763),console.log("The result is: "+result);

As you can see, the code is now minified and difficult to read or debug. However, we can use a source map to map the compiled code back to the original source code and debug it as we would normally.

To enable source map support, we need to add a special comment to the minified code that tells the browser where to find the source map file. We add the following comment to the end of the minified code:

//# sourceMappingURL=app.min.js.map

This tells the browser that there is a source map file for the minified code-named “app.min.js.map.”

Now, when we open the HTML file in the browser and inspect the code using the browser's developer tools, we can enable source map support and view the original source code. Here's how to do it:

  1. Open the developer tools in your browser and navigate to the "Sources" tab.
  2. Find the minified JavaScript file and click on it to open it in the editor.
  3. In the bottom right corner of the editor, click on the gear icon and select "Enable source maps".
  4. Reload the page to see the original source code.

Now we can set breakpoints, examine variables, and step through the code as we would normally, with the added benefit of being able to see the original source code.

In our example, we can set a breakpoint on the return statement in the multiply function and examine the values of a and b. We can then step through the code and see the values change as the code executes. This allows us to identify and fix errors in the original source code, even though the code is minified and transpiled.

Debugging with source maps is a powerful technique that makes it easier to debug complex JavaScript applications that use transpilation and minification as compared to other languages. By mapping the compiled code back to the original source code, developers can more easily identify and fix errors, improving the quality and maintainability of their code.

Conclusion

  • Debugging is an important skill for Web developers to master in order to catch and fix errors in their code.
  • There are a variety of tools and techniques that can be used to debug JavaScript code, including console.log, the debugger statement, try-catch statements, browser developer tools, linters, and source maps.
  • There are plenty of resources out there to help you master javascript and debugging in JS.
  • Using these tools and techniques can help you debug your code more efficiently and effectively, and catch errors early in the development process.
  • Using console.log statements to output values to the browser console, allowing you to examine the state of variables and identify issues.
  • Utilizing try-catch statements to handle errors and exceptions in your code makes it easier to identify and fix problems.
  • Using linters to catch syntax errors, unused variables, and code style issues improves the maintainability and quality of your code.
  • Utilizing source maps to map errors and warnings in the compiled code back to the original source code, making it easier to debug minified or transpiled code.
  • Remember to stay organized and methodical when debugging, and always test your code thoroughly to ensure that it is working as intended.


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1 year, 4 months ago  -  @radhika-keni   

@neji_14 :Thanks so mcuh for the fantastic post .
A quick question though - How to we make sure the colab session does not terminate ? If the colab session terminates , the steamlit app hosted through colab is no longer up and serving requests ! Your response would be much appreciated !!

😀 | ☹️     Reply

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Shivam Bhatele

Software Developer, Scaler

@shivambhatele80
I am a Software Developer and I loved to share programming knowledge and interact with new people. My hobbies are coding, reading books, and learning new things.
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