Convert JSON to YAML in JavaScript/Node.js [Complete Guide]

Install js-yaml

JavaScript doesn't have built-in YAML support (though it has native JSON with JSON.parse()). Install the js-yaml library, the most popular npm package for JSON to YAML conversion. Prefer a different language? Check our Python, Java, or Go guides.

# Install js-yaml using npm
npm install js-yaml

# Or using yarn
yarn add js-yaml

# Verify installation
npm list js-yaml

js-yaml supports YAML 1.2 specification and is used by thousands of projects including ESLint, Webpack, and many others.

Convert JSON to YAML (Node.js)

Here's how to convert JSON to YAML in Node.js:

Basic Conversion

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

// Your JSON data (or any JavaScript object)
const jsonData = {
  name: "my-app",
  version: "1.0.0",
  dependencies: {
    express: "^4.18.0",
    lodash: "^4.17.0"
  },
  scripts: {
    start: "node server.js",
    test: "jest"
  }
};

// Convert to YAML
const yamlString = yaml.dump(jsonData);
console.log(yamlString);

Output:

name: my-app
version: 1.0.0
dependencies:
  express: ^4.18.0
  lodash: ^4.17.0
scripts:
  start: node server.js
  test: jest

ES Modules (import syntax)

import yaml from 'js-yaml';

const jsonData = { name: "example", version: "1.0.0" };
const yamlString = yaml.dump(jsonData);
console.log(yamlString);

Convert YAML to JSON (Node.js)

Converting YAML back to JSON is equally simple:

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

const yamlString = `
name: my-app
version: 1.0.0
database:
  host: localhost
  port: 5432
`;

// Parse YAML to JavaScript object
const jsonData = yaml.load(yamlString);

// Convert to JSON string
const jsonString = JSON.stringify(jsonData, null, 2);
console.log(jsonString);

Browser Usage

js-yaml works in browsers too. Include it via CDN:

Using CDN

<!-- Include js-yaml from CDN -->
<script src="https://unpkg.com/js-yaml@4/dist/js-yaml.min.js"></script>

<script>
  // js-yaml is available as window.jsyaml
  const jsonData = {
    name: "browser-app",
    version: "1.0.0"
  };
  
  // Convert JSON to YAML
  const yamlString = jsyaml.dump(jsonData);
  console.log(yamlString);
  
  // Convert YAML to JSON
  const parsed = jsyaml.load(yamlString);
  console.log(parsed);
</script>

With Bundlers (Webpack, Rollup, Vite)

// Works the same as Node.js when bundled
import yaml from 'js-yaml';

function convertJsonToYaml(jsonData) {
  return yaml.dump(jsonData);
}

function convertYamlToJson(yamlString) {
  return yaml.load(yamlString);
}

Reading and Writing Files

Read JSON File, Write YAML

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

function jsonFileToYaml(inputPath, outputPath) {
  // Read JSON file
  const jsonContent = fs.readFileSync(inputPath, 'utf8');
  const data = JSON.parse(jsonContent);
  
  // Convert and write YAML
  const yamlContent = yaml.dump(data);
  fs.writeFileSync(outputPath, yamlContent, 'utf8');
  
  console.log(`Converted ${inputPath} to ${outputPath}`);
}

// Usage
jsonFileToYaml('config.json', 'config.yaml');

Read YAML File, Write JSON

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

function yamlFileToJson(inputPath, outputPath) {
  // Read YAML file
  const yamlContent = fs.readFileSync(inputPath, 'utf8');
  const data = yaml.load(yamlContent);
  
  // Convert and write JSON
  const jsonContent = JSON.stringify(data, null, 2);
  fs.writeFileSync(outputPath, jsonContent, 'utf8');
  
  console.log(`Converted ${inputPath} to ${outputPath}`);
}

// Usage
yamlFileToJson('config.yaml', 'config.json');

Async/Await Version

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

async function convertJsonToYaml(inputPath, outputPath) {
  const jsonContent = await fs.readFile(inputPath, 'utf8');
  const data = JSON.parse(jsonContent);
  const yamlContent = yaml.dump(data);
  await fs.writeFile(outputPath, yamlContent, 'utf8');
}

// Usage
convertJsonToYaml('data.json', 'data.yaml')
  .then(() => console.log('Done!'))
  .catch(err => console.error(err));

Advanced Options

js-yaml's dump() function accepts options for customizing output:

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

const data = {
  name: "example",
  items: [1, 2, 3],
  nested: { a: 1, b: 2 }
};

// Custom formatting options
const yamlString = yaml.dump(data, {
  indent: 4,           // Indentation spaces (default: 2)
  lineWidth: 80,       // Max line width (default: 80)
  noRefs: true,        // Don't use anchors/aliases
  sortKeys: true,      // Sort object keys alphabetically
  quotingType: '"',    // Quote style (single or double)
  forceQuotes: false   // Force quotes around all strings
});

console.log(yamlString);

Common Errors and Solutions

Error Handling Example

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

function safeConvert(inputPath, outputPath) {
  try {
    const content = fs.readFileSync(inputPath, 'utf8');
    const data = JSON.parse(content);
    const yamlContent = yaml.dump(data);
    fs.writeFileSync(outputPath, yamlContent, 'utf8');
    return { success: true };
  } catch (error) {
    if (error instanceof SyntaxError) {
      return { success: false, error: 'Invalid JSON syntax' };
    }
    if (error.code === 'ENOENT') {
      return { success: false, error: 'File not found' };
    }
    return { success: false, error: error.message };
  }
}