Typescript Builder Pattern (Generic to Specific Implementation)

BlogPostViewModelBuilder.ts

import { injectable } from 'inversify';
import BuilderBase from './BuilderBase';

import IBlogPostViewModelBuilder from './IBlogPostViewModelBuilder';

import IBlogPostViewModel from '@g33kchris/g33kchris.dto.ui/IBlogPostViewModel';
import IContentHeroViewModel from '@g33kchris/g33kchris.dto.ui/IContentHeroViewModel';
import IContentBodyViewModel from '@g33kchris/g33kchris.dto.ui/IContentBodyViewModel';
import IContentMetaViewModel from '@g33kchris/g33kchris.dto.ui/IContentMetaViewModel';
import IRelatedContentViewModel from '@g33kchris/g33kchris.dto.ui/IRelatedContentViewModel';
import IPostsCollectionViewModel from '@g33kchris/g33kchris.dto.ui/IPostsCollectionViewModel';
import BlogPostViewModel from '@g33kchris/g33kchris.dto.ui/BlogPostViewModel';

// Concrete implementation of the Builder

@injectable()
export class BlogPostViewModelBuilder implements IBlogPostViewModelBuilder {

    private _builder: BuilderBase<IBlogPostViewModel>; // <= Leverages the generic BuilderBase to build up an object.

    constructor() {
        this._builder = new BuilderBase<IBlogPostViewModel>(BlogPostViewModel);
    }

    withAvailable(available: boolean): IBlogPostViewModelBuilder {
        this._builder
            .with(vm => Object.assign({}, vm, { available })); // <= Build expressions!
        return this;
    }
    withHero(hero: IContentHeroViewModel): IBlogPostViewModelBuilder {
        this._builder
            .with(vm => Object.assign({}, vm, { hero }));
        return this;
    }
    withBody(body: IContentBodyViewModel): IBlogPostViewModelBuilder {
        this._builder
            .with(vm => Object.assign({}, vm, { body }));
        return this;
    }
    withMeta(meta: IContentMetaViewModel): IBlogPostViewModelBuilder {
        this._builder
            .with(vm => Object.assign({}, vm, { meta }));
        return this;            
    }
    withRelated(related: IRelatedContentViewModel): IBlogPostViewModelBuilder {
        this._builder
            .with(vm => Object.assign({}, vm, { related }));
        return this;
    }
    withOtherPosts(otherPosts: IPostsCollectionViewModel): IBlogPostViewModelBuilder {
        this._builder
            .with(vm => Object.assign({}, vm, { otherPosts }))
        return this;
    }
    build(): IBlogPostViewModel {
        return this._builder.build();
    }
}

BuilderBase.ts

import IBuilderBase from './IBuilderBase';

export default class BuilderBase<T> implements IBuilderBase<T> {

    private _actions: Array<(result: T) => T> = []; // <= This holds an array of build expressions to run on build

    private _result: T;

    constructor(type: { new(): T }){
        // This will new us up an instance of an object without having to know the type!
        // https://stackoverflow.com/questions/17382143/how-to-create-a-new-object-from-type-parameter-in-generic-class-in-typescript
        this._result = new type();
    }

    with(action: (result: T) => T): IBuilderBase<T> {
        this._actions.push(action);
        return this;
    }

    build(): T {
        for (let a of this._actions) {
            this._result = a(this._result);
        }

        return this._result;
    }
}

IBlogPostViewModelBuilder.ts

import IContentHeroViewModel from '@g33kchris/g33kchris.dto.ui/IContentHeroViewModel';
import IContentBodyViewModel from '@g33kchris/g33kchris.dto.ui/IContentBodyViewModel';
import IContentMetaViewModel from '@g33kchris/g33kchris.dto.ui/IContentMetaViewModel';
import IRelatedContentViewModel from '@g33kchris/g33kchris.dto.ui/IRelatedContentViewModel';
import IPostsCollectionViewModel from '@g33kchris/g33kchris.dto.ui/IPostsCollectionViewModel';
import IBlogPostViewModel from '@g33kchris/g33kchris.dto.ui/IBlogPostViewModel';

// Introductory Builder Pattern implementation (very specific build members)

export default interface IBlogPostViewModelBuilder {

    withAvailable(available: boolean): IBlogPostViewModelBuilder;

    withHero(hero: IContentHeroViewModel): IBlogPostViewModelBuilder;

    withBody(body: IContentBodyViewModel): IBlogPostViewModelBuilder;

    withMeta(meta: IContentMetaViewModel): IBlogPostViewModelBuilder;

    withRelated(related: IRelatedContentViewModel): IBlogPostViewModelBuilder;

    withOtherPosts(withOtherPosts: IPostsCollectionViewModel): IBlogPostViewModelBuilder;

    build(): IBlogPostViewModel;
}

IBuilderBase.ts

// An interface to build an implementation of the BuilderBase

export default interface IBuilderBase<T> {
    with(action: (result: T) => T): IBuilderBase<T> ;

    build(): T;
}