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Node.js Design Patterns

Builder Pattern: Implementing a URL Object Builder

Explore the Builder pattern by implementing a URL object builder in Node.js. Understand how to simplify object construction with setter methods, ensure consistent and valid URL instances, and improve code readability when managing complex URL components.

We'll cover the following...

We want to implement a Url class that can hold all the components of a standard URL, validate them, and format them back into a string. This class is going to be intentionally simple and minimal, so for standard production use, we recommend the built-in URL class.

Implementation

Now, let’s implement our custom Url class in a url.js named file.

Node.js
export class Url {
  constructor (protocol, username, password, hostname,
    port, pathname, search, hash) {
    this.protocol = protocol
    this.username = username
    this.password = password
    this.hostname = hostname
    this.port = port
    this.pathname = pathname
    this.search = search
    this.hash = hash
    this.validate()
  }
  validate () {
    if (!this.protocol || !this.hostname) {
      throw new Error('Must specify at least a ' +
        'protocol and a hostname')
    }
  }
  toString () {
    let url = ''
    url += `${this.protocol}://`
    if (this.username && this.password) {
      url += `${this.username}:${this.password}@`
    }
    url += this.hostname
    if (this.port) {
      url += this.port
    }
    if (this.pathname) {
      url += this.pathname
    }
    if (this.search) {
      url += `?${this.search}`
    }
    if (this.hash) {
      url += `#${this.hash}`
    }
    return url
  }
}

A standard URL is made of several components, so to take them all in, the Url class’ constructor is inevitably big. Invoking such a constructor can be a challenge, as we have to keep track of the argument position to know what component of the URL we’re passing. Take a look at the following example to get an idea of this:

return new Url('https', null, null, 'example.com', null, null, null, null)

This is the perfect situation for applying the ...