How to use the command xo (with examples)

The xo command is a pluggable, zero-configuration linting utility for JavaScript. It helps to identify and fix common issues in JavaScript code, ensuring high code quality and adherence to established standards.

Use case 1: Lint files in the “src” directory

Code:

xo

Motivation: With this use case, you can easily lint all the files present in the “src” directory. This is useful when you want to ensure that all the JavaScript files in your project adhere to a predefined set of coding standards and guidelines.

Explanation: In this use case, the command xo is executed without any arguments. This tells xo to lint all the JavaScript files in the current directory and its subdirectories. By default, xo uses the JavaScript Standard Style for linting.

Example output:

file1.js
  1:1  warning  Missing "use strict" statement  strict
  2:1  warning  Strings must use singlequote     quotes

file2.js
  1:1  warning  Missing "use strict" statement  strict

✖ 3 problems (0 errors, 3 warnings)
    1 error
    2 warnings

Use case 2: Lint a given set of files

Code:

xo file1.js file2.js

Motivation: Sometimes, you may only want to lint specific JavaScript files rather than the entire project directory. With this use case, you can specify the exact files you want to lint, allowing you to focus on specific parts of your codebase.

Explanation: In this use case, the command xo is followed by the names of the files you want to lint. This tells xo to only lint the specified files and ignore the rest.

Example output:

file1.js
  1:1  warning  Missing "use strict" statement  strict
  2:1  warning  Strings must use singlequote     quotes

file2.js
  1:1  warning  Missing "use strict" statement  strict

✖ 3 problems (0 errors, 3 warnings)
    1 error
    2 warnings

Use case 3: Automatically fix any lint issues found

Code:

xo --fix

Motivation: While linting helps identify issues in your code, manually fixing all the issues can be time-consuming and error-prone. With this use case, you can let xo automatically fix most of the lint issues, saving you time and effort.

Explanation: In this use case, the --fix flag is added to the xo command. This tells xo to automatically fix any lint issues it finds. xo will attempt to fix as many issues as it can, while providing a report of the changes made.

Example output:

file1.js
  ✖ 1:1  Missing "use strict" statement  strict  xo/strict

✖ 1 problem (0 errors, 1 warning)

file1.js
  ✓ 1:1  Added missing "use strict" statement  strict  xo/strict

✖ 1 problem (0 errors, 1 warning)

Use case 4: Lint using spaces as indentation instead of tabs

Code:

xo --space

Motivation: In JavaScript development, the choice between using spaces or tabs for indentation is a common debate. With this use case, you can enforce the use of spaces for indentation, ensuring consistent code formatting across your project.

Explanation: In this use case, the --space flag is added to the xo command. This tells xo to use spaces for indentation instead of tabs. By default, xo uses tabs for indentation. Using the --space flag overrides this behavior.

Example output:

file1.js
  2:5  error  Expected to be indented by 2 spaces  indent

✖ 1 problem (1 error, 0 warnings)

Use case 5: Lint using the “prettier” code style

Code:

xo --prettier

Motivation: In addition to enforcing coding standards, it is common to use code formatters to ensure consistent code style and formatting. With this use case, you can let xo lint your JavaScript code using the “prettier” code style, further enhancing code readability and maintainability.

Explanation: In this use case, the --prettier flag is added to the xo command. This tells xo to use the “prettier” code style for linting. Prettier is a popular code formatter that automatically formats JavaScript code based on a predefined set of rules.

Example output:

file1.js
  2:5  error  Delete `·`  prettier/prettier

✖ 1 problem (1 error, 0 warnings)

Conclusion:

The xo command serves as a powerful linting utility for JavaScript development. By using the various use cases mentioned above, you can ensure that your JavaScript code adheres to coding standards, automatically fix lint issues, and enforce consistent code style and indentation. With xo, you can maintain high code quality and improve the overall readability and maintainability of your JavaScript projects.