Working with YAML in JavaScript (Node.js): parsing, generation and validation

Working with YAML in JavaScript (Node.js): complete guide

YAML (YAML Ain't Markup Language) is a human-readable data serialization format widely used for configuration files, API descriptions, CI/CD pipelines, and data exchange. In the Node.js ecosystem, there are several powerful libraries for working with YAML. In this article, we will thoroughly examine the main tools, their capabilities, and usage examples.

Popular libraries for YAML in Node.js

The most common libraries for working with YAML in the Node.js environment:

• js-yaml — the most popular and actively maintained library. Supports a full range of operations: parsing, serialization, custom schemas and types.
• yaml (yaml package) — a modern alternative with support for strict parsing, comments, and AST (abstract syntax tree).
• yamljs — a lightweight library with a simple API, suitable for basic tasks.

Installing the js-yaml library

To start working with YAML in Node.js, install the library via npm:

npm install js-yaml

After installation, import the library into your project:

const yaml = require('js-yaml');const fs = require('fs');

Parsing YAML into a JavaScript object

The main operation is converting a YAML string into a JavaScript object:

const yamlString = `server:  host: localhost  port: 8080  ssl: truedatabases:  - name: users    type: postgres  - name: logs    type: mongodb`;

try {  const data = yaml.load(yamlString);  console.log(data.server.host); // "localhost"  console.log(data.databases[0].name); // "users"} catch (e) {  console.error('YAML parsing error:', e.message);}

The yaml.load() method safely converts a YAML string into an object. To load from a file, use:

try {  const config = yaml.load(fs.readFileSync('config.yaml', 'utf8'));  console.log(config);} catch (e) {  console.error('Error reading configuration:', e);}

Serializing a JavaScript object to YAML

The reverse operation is converting an object into a YAML string:

const configObject = {  app: {    name: "MyApp",    version: "1.0.0"  },  features: ["auth", "logging", "analytics"],  database: {    host: "db.example.com",    port: 5432  }};

const yamlString = yaml.dump(configObject, {  indent: 2,  lineWidth: 120,  noRefs: true});

console.log(yamlString);// Output:// app://   name: MyApp//   version: 1.0.0// features://   - auth//   - logging//   - analytics// database://   host: db.example.com//   port: 5432

Parameters of the yaml.dump() method:

• indent — number of spaces for indentation (default 2)
• lineWidth — maximum line length (default 80)
• noRefs — disable the use of anchors and references
• skipInvalid — skip invalid values instead of throwing an error

Working with custom YAML types

js-yaml supports custom schemas and data types. For example, you can add support for dates:

const yaml = require('js-yaml');

// Creating a custom schema with date supportconst schema = yaml.DEFAULT_SCHEMA.extend([  new yaml.Type('tag:yaml.org,2002:timestamp', {    kind: 'scalar',    resolve: (data) => {      return !isNaN(Date.parse(data));    },    construct: (data) => {      return new Date(data);    },    instanceOf: Date,    represent: (date) => {      return date.toISOString();    }  })]);

const yamlString = 'event_date: 2024-03-15T14:30:00Z';const parsed = yaml.load(yamlString, { schema });console.log(parsed.event_date inst