Node.js Design Patterns/

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Builder Pattern: Implementing a URL Object Builder

Builder Pattern: Implementing a URL Object Builder

Learn the implementation details of a URL object builder.

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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.

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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 ...