# Testing, validating, and linting

## Before you begin

For the best results editing and testing browser compat data, you need the following:

- A familiarity with your terminal and Git (for example, you know how to switch directories, clone a repository, and run scripts)
- A text editor (or editor extension) that supports [EditorConfig](https://editorconfig.org/) and the project's [`.editorconfig` file](../.editorconfig)
- Node.js, with [an Active LTS or more recent release](https://nodejs.org/en/download/)

## Install dependencies

Install the dependencies from npm. From the top-level project directory, run `npm install`.

Dependencies change from time to time. Periodically re-run `npm install` to get the latest dependencies.

## Validate the data

All data must conform to the schema, plus several additional consistency and style checks. To test your changes locally, run `npm test`.

For more information on the schema for feature data, see [`compat-data-schema.md`](../schemas/compat-data-schema.md) and [`compat-data.schema.json`](../schemas/compat-data.schema.json).

For more information on the schema for browser data, see [`browsers-schema.md`](../schemas/browsers-schema.md) and [`browsers.schema.json`](../schemas/browsers.schema.json).

## Generate statistics

To see how changes will affect the statistics of exact (formerly "real") and ranged values, you can run `npm run stats [folder]`. This generates a Markdown-formatted table of the percentages of exact and ranged values for the eight primary browsers that browser-compat-data is focusing on. The script also takes an optional argument regarding a specific folder (such as `api` or `javascript`), which will print statistics result for only that folder. Additionally, you can run the script with `--all` to get statistics for all browsers tracked in BCD, not just the primary eight.

> [!NOTE]
> Originally, this script was designed to track "real" (either `false` or a version number, as defined in [issue 3555](https://github.com/mdn/browser-compat-data/issues/3555)), ranged, true, and null values in order to track the progress of a project to eliminate "non-real" (true and null) values. Since the project was completed, the script was simplified to display just exact and ranged values.

## Traverse features

To find all the entries that are of a specified value, you can run `npm run traverse -- [options] [folder]`.

By default, the script will traverse and print the dotted path to every feature. One or more positional arguments can limit the traversal to a specific folder (for example, `api`). Additional options can limit the features listed to features with data matching specific browser and version values.

Run `npm run traverse -- --help` for a complete list of options and examples.

The `-b` or `--browser` argument may be any browser in the [`browsers/` folder](https://github.com/mdn/browser-compat-data/blob/main/browsers/). This argument may be repeated to traverse multiple browsers. By default, the script will traverse all browsers.

The `-f` or `--filter` argument may be any value accepted by `version_added` or `version_removed`. This argument may be repeated to test multiple values. By default, the script will traverse all features regardless of their value.

Examples: to search for all Safari entries that are not supported, run `npm run traverse -- -b safari -f false`. To search for all WebView entries that are mirroring from upstream in `api` and `javascript`, run `npm run traverse api,javascript -- -b webview_android -f mirror`. To search for all Firefox entries supported since `10` across all folders, run `npm run traverse -- -b firefox -f 10`.