Introduction to js-yaml

js-yaml is an awesome library for parsing and dumping YAML in JavaScript. It allows for easy manipulation and conversion of YAML data to JavaScript objects and vice versa. With a wide range of APIs, js-yaml makes working with YAML a seamless experience.

Basic Usage

1. Parsing YAML to JavaScript Object

  const yaml = require('js-yaml');
  const fs = require('fs');
  
  try {
    const doc = yaml.load(fs.readFileSync('document.yaml', 'utf8'));
    console.log(doc);
  } catch (e) {
    console.log(e);
  }

2. Dumping JavaScript Object to YAML

  const yaml = require('js-yaml');
  
  const obj = { name: 'John', age: 30, city: 'New York' };
  const yamlStr = yaml.dump(obj);
  
  console.log(yamlStr);

3. Schema Customization

  const yaml = require('js-yaml');
  
  const CUSTOM_SCHEMA = yaml.DEFAULT_SCHEMA.extend({
    implicit: [new yaml.Type('!date', {
      kind: 'scalar',
      resolve: data => /\d{4}-\d{2}-\d{2}/.test(data),
      construct: data => new Date(data)
    })]
  });

  const data = yaml.load('birthday: 1990-01-01', { schema: CUSTOM_SCHEMA });
  console.log(data.birthday.toISOString());

4. Creating Custom YAML Types

  const yaml = require('js-yaml');
  
  const PointType = new yaml.Type('!point', {
    kind: 'scalar',
    construct: data => data.split(',').map(Number),
    instanceOf: Array,
  });

  const schema = yaml.Schema.create([ PointType ]);

  const doc = yaml.load('point: 1,2,3', { schema: schema });
  console.log(doc);

Advanced Techniques

5. Using Safe Load and Safe Dump

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

  // Load a YAML document safely
  const doc = yaml.safeLoad(fs.readFileSync('input.yaml', 'utf8'));

  // Dump a JavaScript object safely
  const yamlStr = yaml.safeDump(doc);
  
  console.log(yamlStr);

6. Error Handling

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

  try {
    const doc = yaml.load('invalid: yaml:');
  } catch (e) {
    console.error(e.message);
  }

Application Example

Let’s create an example application that reads a YAML file, modifies the data, and writes it back to a YAML file. We will use several APIs demonstrated above.

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

  // Read data from YAML file
  let data;
  try {
    data = yaml.load(fs.readFileSync('input.yaml', 'utf8'));
  } catch (e) {
    console.error('Error reading YAML file:', e);
    return;
  }

  // Modify the data
  data.age += 1;

  // Write data back to YAML file
  try {
    fs.writeFileSync('output.yaml', yaml.dump(data));
    console.log('Data written to output.yaml:', data);
  } catch (e) {
    console.error('Error writing YAML file:', e);
  }

By utilizing js-yaml, we can easily manage YAML data within our JavaScript applications, making it a powerful tool for configuration and data serialization.

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