builder-pattern

Create a builder pattern for Typescript using ES6 proxy.

Installation

yarn add builder-pattern

Usage

Basic usage

interface UserInfo {
  id: number;
  userName: string;
  email: string;
}

const userInfo = Builder<UserInfo>()
                   .id(1)
                   .userName('foo')
                   .email('[email protected]')
                   .build();

To get value from existing builder, just call the method without parameter, current value will be returned.

const builder = Builder<UserInfo>();

builder.id(1);
console.log(builder.id());        // 1

console.log(builder.userName());  // undefined
builder.userName('foo');
console.log(builder.userName());  // foo

const userInfo = builder.build();

A note of caution: when building objects from scratch, the builder currently cannot ensure that all mandatory fields have been set. The built object might thus violate the contract of the given interface. For example, the following will compile (see also the example in the tests):

const brokenUserInfo = Builder<UserInfo>()
                         .build();

A way around this is to use template objects (see Usage with template objects).

Another way is to use StrictBuilder (see Usage with StrictBuilder).

Usage with template objects

You can also specify a template object, which allows easy creation of variation of objects. This is especially useful for making test data setup more readable:

const defaultUserInfo: UserInfo = {
  id: 1,
  userName: 'foo',
  email: '[email protected]'
};

const modifiedUserInfo = Builder(defaultUserInfo)
                          .id(2)
                          .build();

Notes:

• With this approach, if the template object conforms to the interface, the built object will, too.
• The builder will effectively create and modify a shallow copy of the template object.

Usage with class object

You can also specify a class object.

class UserInfo {
  id!: number;
  userName!: string;
  email!: string;
}

const userInfo = Builder(UserInfo)  // note that ( ) is used instead of < > here
                   .id(1)
                   .userName('foo')
                   .email('[email protected]')
                   .build();

Moreover, you can also specify a class object with a template object.

class UserInfo {
  id!: number;
  userName!: string;
  email!: string;
}

const userInfo = Builder(UserInfo, {id: 1, userName: 'foo'})
                   .userName:('foo bar')
                   .email('[email protected]')
                   .build();

Usage with override objects

You can specify a override object, which allows override values when calling build(). This is useful for some cases:

const overrideUserInfo: Partial<UserInfo> = {
  email: '[email protected]'
};

const userInfo = Builder(null, overrideUserInfo)
                   .id(1)
                   .userName('foo')
                   .email('[email protected]')
                   .build();  // email will be overrided when calling build()
                   
console.log(userInfo);  // { id: 1, userName: 'foo', email: '[email protected]' }

Usage with StrictBuilder

StrictBuilder is used to make sure all variables are initialized.

interface UserInfo {
  id: number;
  userName: string;
  email: string;
}

const userInfo = StrictBuilder<UserInfo>()
                   .id(1)
                   .build(); // This expression is not callable.
                             // Type 'never' has no call signatures.ts(2349)

All variables must be initialized before calling build().

const userInfo = StrictBuilder<UserInfo>()
                   .id(1)
                   .userName('foo')
                   .email('[email protected]')
                   .build();  // build() is called successfully

Notes: StrictBuilder does not support template object nor class.

Contributing

1. Fork it!
2. Create your feature branch: git checkout -b my-new-feature
3. Commit your changes: git commit -am 'Add some feature'
4. Push to the branch: git push origin my-new-feature
5. Submit a pull request :D

Credits

The idea is by unional and jcalz. Please refer to the stackoverflow question.

License

This project is licensed under the MIT License - see the LICENSE file for details