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Željko Šević
Željko Šević

Posted on • Originally published at sevic.dev on

Documenting JavaScript code with JSDoc

JSDoc provides adding types to the JavaScript codebase with appropriate conventions inside comments so different IDEs like Visual Studio Code can recognize defined types, show them and make coding easier with auto-completion. Definitions are put inside /** */ comments.

Examples

Custom types can be defined with @typedef and @property tags. Every property has a type and if the property is optional, its name is put between square brackets, and a description can be included after the property name. Global types should be defined in *.jsdoc.js files so they can be used in multiple files without importing. * represents any type.

/**
 * @typedef {object} CollectionItem
 * @property {string} [collectionName] - collection name is optional string field
 * @property {boolean} isRevealed - reveal status
 * @property {number} floorPrice - floor price
 * @property {?string} username - username is a nullable field
 * @property {Array.<number>} prices - prices array
 * @property {Array.<string>} [buyers] - optional buyers array
 * @property {Array.<Object<string, *>>} data - some data
 */
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Classes are auto recognized so @class and @constructor tags can be omitted.

/**
 * Scraper for websites
 */
class Scraper {
  /**
   * Create scraper
   * @param {string} url - website's URL
   */
  constructor(url) {
    this.url = url;
  }
  // ...
}
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Comments starting with the description can omit @description tag. Function parameters and function return types can be defined with @param and @returns tags. Multiple return types can be handled with | operator. Deprecated parts of the codebase can be annotated with @deprecated tag.

/**
 * Gets prices list
 * @private
 * @param {Array.<number>} prices - prices array
 * @returns {string|undefined}
 */
const getPricesList = (prices) => {
  if (prices.length > 0) return prices.join(',');
};

/**
 * Get data from the API
 * @deprecated
 * @returns {Promise<CollectionItem>}
*/
const getData = async () => {
  // ...
};
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Variable types can be documented with @type tags and constants can utilize @const tags.

/**
 * Counter for the requests
 * @type {number}
 */
let counter;

/**
 * HTTP timeout in milliseconds
 * @const {number}
*/
const HTTP_TIMEOUT_MS = 3000;
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Enums can be documented with @enum and @readonly tags.

/**
 * Some states
 * @readonly
 * @enum {string}
 */
const state = {
  STARTED: 'STARTED',
  IN_PROGRESS: 'IN_PROGRESS',
  FINISHED: 'FINISHED',
};
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Docs validation

Linter can validate the docs. Add the following package and update the linter configuration file.

npm i -D eslint-plugin-jsdoc
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// .eslintrc.js
module.exports = {
  extends: ['plugin:jsdoc/recommended'],
};
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Run the linter and it will show warnings if something has to be improved.

Generating the docs overview

Run the following command to recursively generate the HTML files with the docs overview, including the README.md and package.json content. Symbols marked with @private tags will be skipped.

npx jsdoc src -r --destination docs --readme ./README.md --package ./package.json
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This command can be included in the CI/CD pipeline, it depends on the needs of the project.

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