What is Diff - Understanding Code Diff Tools

What is a diff tool?

When we’re writing code, sometimes we want to compare two similar but different files. Diff tools, short for difference, allow programmers to look at the two files side by side and see exactly what differentiates them—where new lines of code have been added; if variable names have been changed; or if any lines of code have been removed.

Most often, we use diff tools to compare two different versions of the same code, usually an older version and a newer version. We could also compare our code to someone else’s code.

Types of diff tools

Diff tools can be classified based on how they’re accessed and integrated into workflows as follows:

• Online diff tools: Browser-based tools that don’t require installation.
• Desktop diff tools: Dedicated software available for systems like Windows or macOS.
• Integrated version control diff tools: Tools that work directly within systems like Git for code tracking and collaboration.

Online diff tools

Online diff tools are ideal for quick comparisons without the hassle of downloading software. They’re perfect for users working on restricted devices or needing instant results. Some examples of these types of diff tools are:

• Diffchecker: Compares text, PDFs, and images with a clean interface and privacy features.

• Mergely: Offers real-time, side-by-side comparisons with support for code and embeddable widgets.

• Draftable: Compares Word, PDF, and other business files with secure, side-by-side viewing.

Desktop diff tools

For those needing more robust functionality or offline access, desktop applications offer advanced features.

For Windows:

• WinMerge: Open-source tool for file/folder comparison and merging.

• Beyond Compare: Advanced sync and comparison features, including FTP support.

For Mac:

• DiffMerge: Provides visual comparisons and merge tools for files and folders.

• Kaleidoscope: Sleek UI with support for text and image comparisons.

Integrated version control diff tools

Version control systems like Git come with built-in diff tools and also support third-party integrations for enhanced comparison.

• Git diff: Built-in command to show changes between commits or branches.

• Meld: Visual diff and merge tool that integrates with Git for side-by-side comparison.

Choosing the right diff tool depends on your workflow needs—whether it’s quick online checks or detailed version control comparisons.

How Codecademy uses diff tools

On Codecademy, we use diffing to show you the differences between the code that you’ve written in the lesson workspace and the final solution code.

Here’s what it looks like to use the Codecademy solution diff tool:

In this example, we have two files:

• On the left, the code you’ve written in main.js
• On the right, the final solution code

Note: It’s ok if you’re not familiar with JavaScript, you don’t need to know it in order to understand how this works.

Here are the three things that can tell you what you need to change in order to make your code the same as the solution:

• Colors: The first thing you’ll notice is that the code that’s different from the solution is shown in red, while the solution code is shown as green. Red indicates the lines that contain code that need to be removed, and green indicates the lines that contain things that need to be added.

• Minus and plus signs: Just like the colors, the minus signs show what lines need to be removed and the plus signs show what lines need to be added.

• Highlighting: Highlights on specific parts let us know if a character or word is different between the files.

In the example above, notice that for the variable listitem, the i was not capitalized in item. However, in the solution, when that variable is used, it is capitalized. The lowercase i in your code and the uppercase I in the solution code are both highlighted. We can also see that the code that is missing from your file is highlighted in the solution code. You forgot to add a const before our variable, so const is highlighted in the solution.

Now that you know what the differences are between your code and the solution, you can edit your code (directly in the diff view) so that it matches what is expected, or choose to replace your code with the solution code. If you use the diffing tool again, you’ll note that the color, the minus and plus signs, and the highlighting have all been removed. The two files are now identical!

Limitations of diff tools

While diffing tools are really helpful, they’re not foolproof. Here are a few challenges you may encounter when using them:

• Code looks different but it still passes: You may write some code that passes a checkpoint, but you’re curious as to whether it matches the solution. It may not! There are often many ways to write a program and we write our evaluation tests to be flexible so all correct code passes an exercise. Don’t be surprised if your code looks different from ours but still works.

• Solution code is for ALL checkpoints: Remember that if you use the diffing tool before you’ve tried to complete all the checkpoints, it will show you the entire solution, not just the solution for the checkpoint you’re on. If you don’t want spoilers, keep trying your best until you reach the last checkpoint!

• Solution code doesn’t work in all cases: Diff tools typically compare changes between versions of files in a code editor. However, they may not be effective in scenarios where outputs or interactions happen outside of editable files, such as in terminals or consoles. For example, if a task involves typing commands or producing printed output, the diff tool may not capture or assess that activity correctly, since it only tracks changes made within the code files.

Conclusion

Diff tools are an essential feature for programmers to visually track the differences between code versions, making the debugging and learning process more efficient. While these tools provide valuable feedback, it’s important to be aware of their limitations and the various ways code can still work despite differences.

For a deeper dive into developer tools, check out Codecademy’s Learn Python Developer Tools with VS Code course to further enhance your coding skills with hands-on experience.

Frequently asked questions

1. What is the purpose of using a diff tool in coding?

A diff tool helps developers compare two different versions of the same code to identify changes, additions, or deletions. It highlights the differences, allowing programmers to see what has been modified and easily update their code accordingly.

2. Can a diff tool be used for all types of code files?

While diff tools are effective for comparing code in most text files, they might not work well with code evaluated in terminals or consoles. For instance, the tool can only compare files within code editors, not outputs from terminal commands.

3. Why does my code look different from the solution even though it works?

In programming, there are often multiple valid ways to solve the same problem. Even if your code looks different from the provided solution, it can still be correct as long as it produces the intended output. Diff tools are designed to highlight differences in code structure or syntax, not necessarily correctness. A difference flagged by a diff tool might simply reflect an alternative approach, not an error.