How to add JavaScript Breakpoint for Effective Debugging

How to add JavaScript Breakpoint for Effective Debugging

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Are you tired of spending hours on how to add JavaScript breakpoints for effective debugging?

Look no further because, in this article, we’ll show you how to add breakpoints and make the process much easier in your JavaScript code!

Continue reading! So that you won’t miss out on this opportunity to improve your debugging skills!

With this guide, you’ll be able to quickly identify and fix issues in your code, saving you time and frustration.

What is breakpoint in JavaScript?

A breakpoint in JavaScript serves as a deliberate stopping or pausing point within a program, primarily utilized for debugging purposes.

It allows developers to temporarily halt the execution of their code at specific locations and inspect the program’s current state.

This feature proves invaluable when trying to identify and resolve issues within the code.

In a simple understanding, a breakpoint in JavaScript is a designated spot in the code where the debugger will automatically halt the execution of the program.

There are several types of breakpoints available in DevTools. Each type of breakpoint has its use case and can be set in different ways.

For instance, a line-of-code breakpoint is used when you know the exact region of code that you need to investigate and can be set by clicking on the line number column in the Sources tab of DevTools.

Breakpoints available in DevTools

1. Conditional line-of-code breakpoints

If you want your code to pause and stop running, but only when a certain condition is true, you can use a conditional line-of-code breakpoint.

For example:

function add(x, y) {
let sum = x + y;
return sum;
}

To set a conditional line-of-code breakpoint, right-click on the line number column in the Sources tab of DevTools and select “Add conditional breakpoint.”

Then, enter the expression x > 10 as the condition that evaluates to true or falls. When you run the code and call the add function with x greater than 10, the execution will pause before the second line is run, allowing you to examine the state of your program.

2. DOM change breakpoints

If you need to pause your code at the point where a DOM node or its children are modified, you can utilize a DOM change breakpoint.

This will allow you to inspect and understand the changes happening to the web page’s structure during the execution of your code.

To set a DOM change breakpoint, right-click on a DOM node in the Elements panel and select “Break on” > “Subtree modifications”. For example, if you have the following HTML code:

<ul id="sampleList">
  <li>Item 1</li>
  <li>Item 2</li>
</ul>

When you run the code and modify the subtree of the <ul> element (e.g., by adding or removing <li> elements), the execution will pause, allowing you to examine the state of your program.

3. XHR/Fetch breakpoints

Use an XHR/Fetch breakpoint to pause code when sending an XHR or Fetch request. This allows you to inspect and modify the request before it is sent or the data after it is received.

To set an XHR/Fetch breakpoint, click on the “XHR/fetch Breakpoints” tab in the Sources panel and enter a URL or part of a URL.

For example, if you have code that sends an XHR or Fetch request to https://api.sample.com/data, you can set an XHR/Fetch breakpoint by clicking on the “XHR/fetch Breakpoints” tab and entering /data as the URL pattern.

When you run the code and send an XHR or Fetch request to https://api.sample.com/data, the execution will pause before sending the request, allowing you to examine the state of your program.

4. Event listener breakpoints

Use an event listener breakpoint when you want to pause on the code that runs after an event, such as click, is fired.

To set an event listener breakpoint, click on the “Event Listener Breakpoints” tab in the Sources panel and expand an event category (e.g., “Mouse”) to see a list of events.

let myButton = document.getElementById("myButton");
myButton.addEventListener("click", function() {
console.log("Button clicked!");
});

Then, check an event (e.g., “click”) to set a breakpoint. For example, if you have code that adds a click event listener to a button element:

5. Exception breakpoints

When you want to stop your code at the exact line that throws an exception (whether it’s caught or uncaught), use an exception breakpoint.

For example, if you have code that throws an exception:

function divide(x, y) {
if (y === 0) {
throw new Error("Cannot divide by zero");
}
return x / y;
}

You can set an exception breakpoint by clicking on the “Pause on exceptions” button in the Sources panel.

When you run the code and call the divide function with y equal to 0, the execution will pause when the exception is thrown, allowing you to examine the state of your program.

6.Function breakpoints

To pause code execution whenever a specific function is called, use a function breakpoint. This lets you examine the function’s behavior during runtime.

To set a function breakpoint, right-click on a function name in the Sources panel and select “Add function breakpoint”. For example, if you have the following code in your JavaScript file:

function add(x, y) {
let sum = x + y;
return sum;
}

When you run the code and call the add function, the execution will pause before entering the function, allowing you to examine the state of your program

How to set a JavaScript breakpoint from code?

You can set breakpoints in your code by calling the debugger method within your code. 

debugger;

This is equivalent to a line-of-code breakpoint, except that the breakpoint is set in your code, not in the DevTools UI.

Other web browsers, such as Microsoft Edge, also have similar debugging tools that allow you to set breakpoints in your JavaScript code.

The “debugger” statement is used to activate debugging tools like setting a breakpoint. If there are no debugging tools available, this statement won’t do anything.

How to add breakpoint JavaScript in Chrome?

To add a breakpoint in JavaScript, you can use the debugging tools available in your web browser.

For instance, in Google Chrome, you can use the Chrome DevTools to set breakpoints in your JavaScript code.

Here’s how to set a line-of-code breakpoint in Chrome DevTools:

  1. Click the Sources tab or press Ctrl + Shift + I (Windows) or Cmd + Option + I (Mac) on your keyboard.
  2. Open the file containing the line of code you want to break on.
  3. Go to the line of code or right-click on the line where you want to add a breakpoint and select “Add Breakpoint.
  4. Or you can click the left of the line of code is the line number column.
  5. A blue icon appears on top of the line number column.

Conclusion

In conclusion, this article provides a simple guide for using JavaScript breakpoints to pause the execution of the code and examine the state of the program.

This article explains what breakpoints are, how they can be set in various ways using DevTools, and the different types of breakpoints available.

Also we provide an illustration how to add breakpoints directly in the JavaScript code using the “debugger” statement.

By following this guide, you can improve your debugging skills and efficiently identify and resolve issues with your JavaScript code.

We are hoping that this article provides you with enough information that helps you understand the JavaScript breakpoint.

You can also check out the following article:

Thank you for reading itsourcecoders 😊.

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