How to use the command 'lighthouse' (with examples)
Lighthouse is a powerful open-source tool developed by Google that assists in analyzing web applications and pages to gather modern performance metrics, enhance user experience, and offer actionable insights into developer best practices. It helps developers and businesses improve site performance by pinpointing areas that need optimization, making it an indispensable tool in the modern web development toolkit.
Generate an HTML report for a specific website and save it to a file in the current directory (with examples)
Code:
lighthouse https://example.com
Motivation:
Generating an HTML report is fundamental for developers who need a detailed and visually appealing document to present site performance details. This kind of report will highlight various metrics in an organized format, which can be shared with team members or stakeholders to inform decision-making and prioritization of optimizations.
Explanation:
lighthouse: This is the command-line utility used to execute the Lighthouse analysis.https://example.com: This is the URL of the website that you want to analyze. By including this, Lighthouse conducts a series of audits on the specified site and generates a comprehensive report in HTML format.
Example output:
Upon executing this command, a file named example-com-YYYYMMDD-HHmmss.report.html will appear in the current directory, with detailed sections on Performance, Accessibility, Best Practices, SEO, and Progressive Web App (PWA) considerations.
Generate a JSON report and print it (with examples)
Code:
lighthouse --output json https://example.com
Motivation:
For developers and automated systems that require programmatic access to Lighthouse results, generating and printing a JSON report is invaluable. Such output can be easily parsed by scripts or integrated into dashboards for further analysis, making it conducive to CI/CD environments.
Explanation:
--output json: Specifies that the output file should be in JSON format rather than the default HTML.https://example.com: Again, this specifies the target URL for the Lighthouse analysis.
Example output:
The JSON report will be printed directly to the console/stdout, providing all the data and scores in a structured, machine-readable format useful for further manipulation or storage.
Generate a JSON report and save it to a specific file (with examples)
Code:
lighthouse --output json --output-path path/to/file.json https://example.com
Motivation:
This use case is ideal for situations where the Lighthouse results need to be stored for later reference or further processing. By specifying an output path, the JSON report can be easily accessed by other applications or team members for extended analysis.
Explanation:
--output json: Determines that the output should be in JSON format.--output-path path/to/file.json: Directs Lighthouse to save the report at the specified file path, offering flexibility in file organization and management.
Example output:
A JSON file containing the audit results will be created at the specified path (path/to/file.json), making it simple to locate and utilize the report as needed.
Generate a report using the browser in headless mode without logging to stdout (with examples)
Code:
lighthouse --quiet --chrome-flags="--headless" https://example.com
Motivation:
Using headless mode is crucial in automated testing and continuous integration scenarios where a visible browser window is impractical. Additionally, a quiet mode suppresses unnecessary logs, streamlining the output for better clarity and focus on results.
Explanation:
--quiet: Minimizes logging to stdout, which is beneficial in automated processes where extensive logging is not required.--chrome-flags="--headless": Opens Chrome in headless mode, meaning it runs without a GUI, suitable for environments where display capabilities are limited or not desired.
Example output:
The report will be generated using headless Chrome, and logging output will be significantly reduced, focusing primarily on essential information.
Generate a report, using the HTTP header key/value pairs in the specified JSON file for all requests (with examples)
Code:
lighthouse --extra-headers=path/to/file.json https://example.com
Motivation:
When testing web applications that require specific authorization or custom headers, you may need to provide these headers to Lighthouse. This use case is applicable for auditing content behind login forms or services that depend on API keys or tokens transmitted in headers.
Explanation:
--extra-headers=path/to/file.json: Specifies that additional HTTP headers contained within the defined JSON file should be included in all requests during the Lighthouse audit process.
Example output:
Lighthouse will analyze https://example.com including any additional headers described in the specified JSON file, potentially revealing performance and accessibility issues arising from those specific conditions or states.
Generate a report for specific categories only (with examples)
Code:
lighthouse --only-categories=performance,accessibility,best-practices,seo,pwa https://example.com
Motivation:
Sometimes, focusing on specific categories of a website is required to conserve time or resources or to prioritize certain areas for improvement. Limiting the audit to chosen categories enhances efficiency, allowing for granular focus on the most pertinent aspects.
Explanation:
--only-categories=performance,accessibility,best-practices,seo,pwa: Directs Lighthouse to execute audits only in the specified categories, selectively evaluating areas such as Performance, Accessibility, Best Practices, SEO, and Progressive Web App capabilities.
Example output:
The generated report will exclusively incorporate detailed scores and advice in the chosen categories, ensuring that the analysis is concentrated where it is moÝt relevant.
Generate a report with device emulation and all throttling disabled (with examples)
Code:
lighthouse --screenEmulation.disabled --throttling-method=provided --no-emulatedUserAgent https://example.com
Motivation:
Disabling throttling and device emulation can be useful for testing the performance of a site in a fully optimized environment, such as on high-speed internal networks or under precise conditions mirroring real-world settings, helping to identify intrinsic issues beyond typical user experiences.
Explanation:
--screenEmulation.disabled: Turns off emulation of screen parameters usually set to mimic mobile devices.--throttling-method=provided: Disables both network and CPU throttling.--no-emulatedUserAgent: Prevents setting the user agent string to that of mobile browsers, allowing the audit to run with the default user agent.
Example output:
The resultant Lighthouse report will reflect site performance under optimal conditions, excluding potential implementation and rendering constraints caused by mobile limitations or throttling.
Display help (with examples)
Code:
lighthouse --help
Motivation:
For users unfamiliar with the Lighthouse command-line options or in need of a reminder on how to use them, accessing the built-in help is an invaluable resource. This provides detailed information about command usage, available options, and syntax.
Explanation:
--help: Displays help information directly in the terminal, elucidating every available command and option within Lighthouse, guiding users on proper usage and offering insight into its capabilities.
Example output:
A comprehensive list of available commands and options in Lighthouse will be presented in the terminal, supplying both novice and seasoned users with the necessary command reference to operate Lighthouse successfully.
Conclusion:
By mastering the various use cases of the Lighthouse command-line tool, developers can substantially improve and tailor their web application analyses. From creating intuitive reports in diverse formats to performing targeted analysis with controlled conditions, Lighthouse provides significant flexibility and insight, elevating the efficacy of web development workflows. Whether you are a seasoned developer or a newcomer to web performance analysis, these examples offer a robust foundation to harness the full potential of Lighthouse for quality web development.
