How to Debug a Node.js Application?
Because it’s quick, simple to use, and permits client-side web programmers to apply their abilities elsewhere, Node.js has grown in popularity over the past ten years. However, creating software is still a difficult endeavor, and eventually, your Node.js code will break. This article demonstrates several techniques that can be used to debug software and identify its root cause.
What is Debugging?
Just like it’s important to know what is node.js is used for before you develop a node.js application, it is vital to understand debugging before you try to debug a node.js program.
The painstaking process of software fixes is referred to as debugging. A fixed character or extra line of code can frequently solve a bug’s problems. Identifying those bugs is another story, and engineers often waste a lot of miserable time attempting to track out the problem.
Thankfully, Node.js offers several excellent features to aid in error tracing. You will typically run into the three types of errors listed below when running a node.js application.
1. Syntax Errors
Your code violates linguistic conventions when, for instance, you leave off the final bracket or spellcheck a phrase incorrectly.
2. Logic Errors
Your code executes, but it does not perform as you had hoped. For instance, a user may not be logged out when requested, a report may have inaccurate data, data may not be entirely stored in a database, etc.
Logic errors can be brought on by:
- Use of an incorrect variable
- Inaccurate assertions, such as if (a > 5) rather than if (a <5)
- Computations that don’t take operator priority into account, like 1+2*3 yielding 7 instead of 9
3. Runtime Errors
When the application is launched is the only time a runtime error becomes apparent, which frequently results in a crash. Runtime problems may result from:
- Splitting by a variable with a value of 0
- Attempting to retrieve a nonexistent array item
- Attempting to modify a read-only file
How to Debug a Node.js Application?
Once you understand what node.js is used for and the common types of error found in a node.js application, you can start to debug the problematic node.js app. Here are some tips to help you get started.
1. Setup a Node Inspector
Thankfully, we can leverage the capabilities of the WebKit-debuggers to operate with our Node.js code by using node-inspector. The actual procedure is easy. Make sure node-inspector is setup first:
A server that essentially says “Hello World” and has a counter is an excellent example app to test out. The first step is to launch your node program with debugging activated, which should display something to stderr like “debugger running on port 5858.” Keep track of the port number because it is the one the debugger is using. Then start node-inspector. You might need to supply your software with a specific port if it utilizes port 8080.
You then launch a WebKit-compatible browser, such as Safari or Chrome, and access debug at 127.0.0.1:8080/port=5858. You must modify the debugger’s port number if it is currently running on a port other than 5858. Additionally, you will need to change port 8080 if the node-inspector receives a customized web port. You will now see a window with the console, scripts, and profiles that is largely empty.
Read- Security Issues with Node.js Development
2. Use the Scripts Tab Appropriately
You can study the call stack and all the regional, closing, and global parameters when the action is halted by a breakpoint or actively halting analysis by hitting the pause button.
To attempt to correct behavior, you can also edit the code. You should be aware that when you change the code using the script tab, the changes are not automatically saved to the file; therefore, you must manually transfer the changes back.
3. Use the Profile Tab
You require the v8-profiler library in order to use the profile tab. Then, inside the program you are debugging, you must need it. Now that the profiles tab has been enabled, all you can do from this window is take a picture of the heap. In order to launch the CPU profiler and choose a more specific place for heap snapshots, you must choose from the code.
Simply insert this code at the desired spot, and you can optionally supply it with a name, to take a stack snapshot. Simply include the code you want to profile with the two lines displayed below to obtain a CPU profile. A name may be added as an option to identify the CPU profile.
Although the APIs provide objects, it is important to note that the node-inspector interface makes it much simpler to browse the data. These tools should help you decide more wisely regarding memory leaks and constraints.
4. Use the Console Tab
Finally, you can use the REPL of a node in the wide scope of your program by using the console tab. There are a few catches because you can’t access local variables because of this. Therefore, the variables that you can read or write were specified without the use of a var declaration.
When you utilize the console, there is one more catch. Log refers to the node console.log, not the console.log for WebKit. This indicates that the output is sent to stdout rather than the console tab. The rest of the time, the node REPL is quite simple.
The simple part is launching a Node-based web application. The harder part is making sure your Node instance keeps serving resources to your program. For this, it is important to keep your node.js application bug free.
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