JS OptionsResolver - Symfony OptionsResolver for JS

The JS OptionsResolver library is Symfony OptionsResolver for JS. It allows you to create an options system with required options, defaults, validation (type, value), normalization and more.

Installation

Browser setup

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Just include OptionsResolver in a script tag. Now you can use it.

<script src="js-optionsresolver.js"></script>

Node

TODO

Usage

Imagine you have a Mailer class which has four options: host, username, password and port:

Mailer = function(options) {
  this.options = options;
};

When accessing the options, you need to add a lot of boilerplate code to check which options are set:

Mailer = function(options) {
  // ...
  this.sendMail = function(from, to) {
    var mail = ...;
    mail.setHost(this.options.host ? this.options.host : "smtp.example.com");
    mail.setUsername(this.options.username ? this.options.username : "user");
    mail.setPassword(this.options.password ? this.options.password : "pa$$word");
    mail.setPort(this.options.port ? this.options.port : 25);

    // ...
  }
}

This boilerplate is hard to read and repetitive. Also, the default values of the options are buried in the business logic of your code. Use the Object.assign to fix that:

Mailer = function(options) {
  this.options = Object.assign({
    host: "smtp.example.com",
    username: "user",
    password: "pa$$word",
    port: 25
  }, options);
}

Now all four options are guaranteed to be set. But what happens if the user of the Mailer class makes a mistake?

var mailer = new Mailer({
  usernme: "johndoe", // usernme misspelled (instead of username)
});

No error will be shown. In the best case, the bug will appear during testing, but the developer will spend time looking for the problem. In the worst case, the bug might not appear until it's deployed to the live system.

Fortunately, the OptionsResolver class helps you to fix this problem:

Mailer = function(options) {
  var resolver = new OptionsResolver();
  resolver
    .setDefaults({
      host: "smtp.example.com",
      username: "user",
      password: "pa$$word",
      port: 25
    });

  this.options = resolver.resolve(options);
}

Like before, all options will be guaranteed to be set. Additionally, an UndefinedOptionsException is thrown if an unknown option is passed:

var mailer = new Mailer({
  usernme: "johndoe"
});

// Uncaught UndefinedOptionsException: The option "usernme" does not exist.
// Know options are: "host", "username", "password", "port"

The rest of your code can access the values of the options without boilerplate code:

Mailer = function(options) {
  this.sendMail = function(from, to) {
    var mail = ...;

    mail.setHost(this.options.host);
    mail.setUsername(this.options.username);
    mail.setPassword(this.options.password);
    mail.setPort(this.options.port);

    // ...
  }
}

Required Options

If an option must be set by the caller, pass that option to setRequired(). For example, to make the host option required, you can do:

Mailer = function(options) {
  var resolver = new OptionsResolver();

  resolver.setRequired("host");
  this.options = resolver.resolve(options);
}

If you omit a required option, a MissingOptionsException will be thrown:

var mailer = new Mailer();

// Uncaught MissingOptionsException: The required options "host" is missing

The setRequired() method accepts a single name or an array of option names if you have more than one required option:

Mailer = function(options) {
  // ...
  resolver.setRequire(["host", "username", "password"]);
}

Use isRequired() to find out if an option is required. You can use getRequiredOptions() to retrieve the names of all required options:

// ...
var requiredOptions = resolver->getRequiredOptions();

If you want to check whether a required option is still missing from the default options, you can use isMissing(). The difference between this and isRequired() is that this method will return false if a required option has already been set:

// ...
resolver.isRequired("host"); // true
resolver.isMissing("host"); // true
resolver.setDefault("host", "smtp.google.com");
resolver.isRequired("host"); // true
resolver.isMissing("host"); // false

The method getMissingOptions() lets you access the names of all missing options.

Type Validation

You can run additional checks on the options to make sure they were passed correctly. To validate the types of the options, call setAllowedTypes():

// ...
// specify one allowed type
resolver.setAllowedTypes("port", "int");

TODO: Specify multiple allowed types and can pass fully qualified class names.

You can pass any type for which an:

• integer (int)
• string (str)
• array (arr)
• boolean (bool)
• float
• object (obj)
• regexp
• function (fn, func)

If you pass an invalid option now, an InvalidOptionsException is thrown:

var mailer = new Mailer({
  port: "465"
});

// Uncaught InvalidOptionsException: The option "port" with "465" is
// expected to be of type "int"

TODO: In sub-classes, you can use addAllowedTypes() to add additional allowed types without erasing the ones already set.

Value Validation

Some options can only take one of a fixed list of predefined values. For example, suppose the Mailer class has a transport option which can be one of sendmail, mail and smtp. Use the method setAllowedValues() to verify that the passed option contains one of these values:

Mailer = function(options) {
  // ...
  resolver
    .setDefault("transport", "sendmail")
    .setAllowedValues("transport", ["sendmail", "mail", "smtp"]);
}

If you pass an invalid transport, an InvalidOptionsException is thrown:

var mailer = new Mailer({
  transport: "send-mail"
});

// Uncaught The option "transport" with value "send-mail" is invalid.
// Accepted values are: "sendmail", "mail", "smtp"

For options with more complicated validation schemes, pass a closure which returns true for acceptable values and false for invalid values:

// ...
resolver.setAllowedValues("transport", function(transport) {
  // return true or false
});

TODO: In sub-classes, you can use addAllowedValues() to add additional allowed values without erasing the ones already set.

Option Normalization

Sometimes, option values need to be normalized before you can use them. For instance, assume that the host should always start with http://. To do that, you can write normalizers. Normalizers are executed after validating an option. You can configure a normalizer by calling setNormalizer():

// ...
resolver.setNormalizer("host", function(options, host) {
  if (!/^https?\:\/\//.test(host)) {
    host = "http://" + host;
  }

  return host;
});

The normalizer receives the actual host and returns the normalized form. You see that the closure also takes an options parameter. This is useful if you need to use other options during normalization:

// ...
resolver.setNormalizer("host", function(options, host) {
  if (!/^https?\:\/\//.test(host)) {
    if (options["encryption"] === "ssl") {
      host = "https://" + host;
    } else {
      host = "http://" + host;
    }
  }

  return host;
});

Default Values that Depend on another Option

Suppose you want to set the default value of the port option based on the encryption chosen by the user of the Mailer class. More precisely, you want to set the port to 465 if SSL is used and to 25 otherwise.

You can implement this feature by passing a closure as the default value of the port option. The closure receives the options as argument. Based on these options, you can return the desired default value:

// ...
resolver.setDefault("encryption", null);
  .setDefault("port", function(options) {
    if (options["encryption"] === "ssl") {
      return 465;
    }

    return 25;
  })

The argument of the callable must be type hinted as options. Otherwise, the callable itself is considered as the default value of the option.

The closure is only executed if the port option isn't set by the user or overwritten in a sub-class.

A previously set default value can be accessed by adding a second argument to the closure:

// ...
resolver.setDefaults({
  encryption: null,
  host: "example.org"
}).setDefault("host", function(options, previousHostValue) {
  if (options["encryption"] === "ssl") {
    return "secure.example.org";
  }

  // Take default value configured in the base class
  return previousHostValue;
});

As seen in the example, this feature is mostly useful if you want to reuse the default values set in parent classes in sub-classes.

Options without Default Values

In some cases, it is useful to define an option without setting a default value. This is useful if you need to know whether or not the user actually set an option or not. For example, if you set the default value for an option, it's not possible to know whether the user passed this value or if it simply comes from the default:

// ...
Mailer = function(options) {
  var resolver = new OptionsResolver();
  resolver.setDefault("port", 25);
  this.options = resolver.resolve(options);

  this.sendMail = function(from, to) {
    // Is this the default value or did the caller of the class really
    // set the port to 25?
    if (this.options["port"] === 25) {
      // ...
    }
  };
}

You can use setDefined() to define an option without setting a default value. Then the option will only be included in the resolved options if it was actually passed to resolve():

// ...
Mailer = function(options) {
  // ...
  resolver.setDefined("port");
  // ...
  this.sendMail = function(from, to) {
    if (this.options["port"]) {
      console.log("Set!");
    } else {
      console.log("Not set");
    }
  }
}

var mailer = new Mailer();
mailer.sendMail();
// => Not set!

var mailer = new Mailer({port: 25});
mailer.sendMail(from, to);
// => Set!

You can also pass an array of option names if you want to define multiple options in one go:

// ...
resolver.setDefined(["port", "encryption"]);

The methods isDefined() and getDefinedOptions() let you find out which options are defined:

// ...
if (resolver.isDefined("host")) {
  // One of the following was called:

  // resolver.setDefault("host", ...);
  // resolver.setRequired("host");
  // resolver.setDefined("host");
}

var definedOptions = resolver.getDefinedOptions();

That's it! You now have all the tools and knowledge needed to easily process options in your code.

Credits

Original documentation for PHP: https://symfony.com/doc/3.4/components/options_resolver.html