Initializing Tredgate Loan App: Vue, TypeScript Guide

Embarking on a new web application project can be an exciting endeavor, especially when leveraging modern frameworks and languages. This comprehensive guide will walk you through the process of initializing the Tredgate Loan app using Vue 3, TypeScript, and a basic loan domain model. This project serves as a practical example for demonstrating how to work with GitHub Copilot in a web application development setting. By the end of this article, you'll have a solid foundation for building a simple yet realistic frontend project without relying on external backends or databases. This approach keeps the focus on frontend development while providing valuable insights into managing application state and business logic within the browser.

High-Level Requirements for Tredgate Loan App

Before diving into the implementation details, let's outline the high-level requirements for the Tredgate Loan application. This will provide a clear roadmap for the development process and ensure that we stay aligned with the project's goals. The primary focus is to create a lean, maintainable application that showcases the capabilities of Vue 3 and TypeScript while adhering to the KISS (Keep It Simple, Stupid) principle. This means avoiding unnecessary complexity and focusing on delivering core functionality in a straightforward manner. The application should manage loan applications with a minimal domain model, making it easy to understand and extend. Data persistence will be handled using localStorage, allowing the application to retain data between sessions without the need for a backend server. This approach simplifies the architecture and allows us to concentrate on the frontend logic. Let's delve deeper into the tech stack and specific requirements to set the stage for a successful implementation.

Tech Stack

The tech stack for the Tredgate Loan app is carefully chosen to provide a modern, efficient, and developer-friendly environment. We'll be using Vite as our build tool, which offers lightning-fast development speeds and optimized production builds. Vue 3, with its composition API, provides a flexible and reactive framework for building user interfaces. TypeScript adds static typing to the mix, enhancing code quality and maintainability. Node.js will be used to run the development server, tests, and tooling, but it won't be part of the production deployment. This stack allows us to leverage the latest web development technologies while keeping the application lightweight and performant. By using these technologies, we aim to create a robust and scalable application that can serve as a valuable learning resource. The combination of Vite, Vue 3, and TypeScript offers a powerful platform for building modern web applications with ease and efficiency. The decision to exclude an external backend or database further simplifies the project, allowing us to focus on frontend development practices and techniques.

Data Handling

One of the key decisions in developing the Tredgate Loan app is how to handle data persistence without relying on an external backend or database. To achieve this, we'll leverage the browser's localStorage API. This allows us to store data directly in the user's browser, ensuring that loan applications persist between sessions. During runtime, all data will live in memory, providing fast access and manipulation. When the application needs to persist data, such as when a new loan application is created or an existing one is updated, we'll serialize the in-memory data and store it in localStorage. When the application starts, it will load data from localStorage into memory, ensuring that the user's loan applications are available. This approach simplifies the application's architecture and reduces the complexity associated with managing a backend server and database. It also aligns with the goal of keeping the application as simple as possible while still demonstrating realistic frontend development scenarios. By using localStorage, we can create a fully functional application that showcases Vue 3, TypeScript, and GitHub Copilot without the overhead of a traditional backend.

Keep It Simple (KISS)

The KISS (Keep It Simple, Stupid) principle is a guiding philosophy for the development of the Tredgate Loan app. This principle emphasizes the importance of simplicity and avoiding unnecessary complexity in design and implementation. In the context of this project, it means focusing on core functionality and avoiding features that add minimal value. The goal is to create an application that is easy to understand, maintain, and extend. This also makes it an ideal platform for demonstrating GitHub Copilot's capabilities in a clear and concise manner. By adhering to the KISS principle, we ensure that the application remains manageable and serves its purpose effectively. This approach also helps to keep the learning curve low, making it easier for developers to grasp the concepts and techniques used in the project. Simplicity in code and architecture leads to fewer bugs, easier debugging, and more efficient collaboration. The Tredgate Loan app, therefore, serves as an excellent example of how to build a robust application by focusing on simplicity and clarity.

Domain Model: TypeScript Definition

To effectively manage loan applications within the Tredgate Loan app, we need to define a clear and concise domain model. This model will be implemented using TypeScript, which provides static typing and enhances code quality. The domain model consists of two main components: the LoanStatus union type and the LoanApplication interface. The LoanStatus type represents the possible states of a loan application, while the LoanApplication interface defines the structure of a loan application object. By defining these types and interfaces, we ensure that our code is well-organized, type-safe, and easy to reason about. This also makes it easier to catch errors early in the development process and reduces the likelihood of runtime issues. The domain model serves as the foundation for the application's data structures and business logic, providing a clear and consistent way to represent loan applications and their attributes. Let's explore the details of each component in the domain model to understand how they contribute to the overall structure of the Tredgate Loan app.

LoanStatus Union Type

The LoanStatus union type is a fundamental part of the Tredgate Loan app's domain model. It defines the possible states that a loan application can be in: 'pending', 'approved', or 'rejected'. By using a union type, we ensure that the status property of a LoanApplication object can only be one of these predefined values. This helps to prevent errors and ensures consistency across the application. TypeScript's type system enforces this constraint, making it easier to catch mistakes during development. The LoanStatus type serves as a clear and concise way to represent the state of a loan application, making the code more readable and maintainable. This also allows us to use type checking to ensure that loan applications are handled correctly based on their status. For example, we can use the LoanStatus type to implement logic that only allows approved loans to be disbursed or rejected loans to be archived. By explicitly defining the possible states of a loan application, we create a more robust and predictable application.

LoanApplication Interface

The LoanApplication interface defines the structure of a loan application object in the Tredgate Loan app. It includes several key properties that describe a loan application, such as the applicant's name, loan amount, term in months, interest rate, status, and creation timestamp. Each property is defined with a specific type, ensuring that the data is consistent and well-structured. The LoanApplication interface serves as a blueprint for creating loan application objects and helps to enforce type safety throughout the application. By defining this interface, we can ensure that all loan applications have the necessary information and that the data is in the correct format. This makes the code more readable, maintainable, and less prone to errors. The properties included in the LoanApplication interface are carefully chosen to represent the essential attributes of a loan application, providing a comprehensive yet concise model for managing loans within the application. This interface also serves as a contract, ensuring that all parts of the application that work with loan applications adhere to the same structure and types.

Business Logic: loanService.ts

The heart of the Tredgate Loan app lies in its business logic, which is encapsulated in the src/services/loanService.ts file. This module contains pure functions that operate on LoanApplication objects and arrays of loans. By keeping the logic pure, we make it easier to test and reason about the code. Each function is designed to perform a specific task, such as creating a loan application, updating its status, or calculating monthly payments. This modular approach enhances code organization and maintainability. The loanService.ts module is designed to be small, easy to read, well-typed, and easy to cover by unit tests. This ensures that the application's core logic is robust and reliable. The functions in this module interact with localStorage to persist data, allowing the application to retain loan applications between sessions. By centralizing the business logic in this module, we create a clear separation of concerns and make it easier to extend the application in the future. Let's dive into the specific functions implemented in loanService.ts to understand how they contribute to the overall functionality of the Tredgate Loan app.

getLoans(): Fetching Loan Applications

The getLoans() function is responsible for retrieving loan applications from localStorage in the Tredgate Loan app. It attempts to load the loans from localStorage using a predefined key (e.g., tredgate_loans). If there is no data stored yet, the function returns an empty array. This ensures that the application starts with a clean slate if no loan applications have been created previously. The function is designed to be simple and efficient, minimizing the overhead of data retrieval. By loading the loan applications from localStorage, the application can persist data between sessions, providing a seamless user experience. This function is a critical part of the application's data management strategy, allowing it to load and display existing loan applications. The use of localStorage simplifies the data storage mechanism and eliminates the need for a backend server or database. The getLoans() function is a key component of the Tredgate Loan app, enabling it to load and manage loan application data effectively.

saveLoans(loans: LoanApplication[]): Persisting Loan Applications

The saveLoans(loans: LoanApplication[]) function is the counterpart to getLoans() in the Tredgate Loan app. It is responsible for persisting an array of LoanApplication objects into localStorage. This function serializes the array of loans and stores it in localStorage using a predefined key. This ensures that the loan applications are saved and can be retrieved later using getLoans(). The function is designed to be straightforward and efficient, minimizing the overhead of data storage. By persisting the loan applications in localStorage, the application can retain data between sessions, providing a consistent user experience. This function is a crucial part of the application's data management strategy, allowing it to save and retrieve loan application data. The use of localStorage simplifies the data storage mechanism and eliminates the need for a backend server or database. The saveLoans() function is a key component of the Tredgate Loan app, enabling it to persist loan application data effectively.

createLoanApplication(...): Creating New Loan Applications

The createLoanApplication(...) function is a core component of the Tredgate Loan app, responsible for creating new loan applications. This function takes an input object containing the applicant's name, loan amount, term in months, and interest rate. It performs basic data validation to ensure that the amount and term are positive numbers and that the applicant's name is not empty. If the validation passes, the function creates a new LoanApplication object with a generated ID, a status of 'pending', and the current ISO timestamp as the creation date. The new loan application is then appended to the existing loans, and the updated array is saved to localStorage. This function encapsulates the logic for creating new loan applications, ensuring that the data is valid and the loan application is properly initialized. By generating a unique ID for each loan application, we can easily identify and manage them within the application. The use of the 'pending' status indicates that the loan application is awaiting review. The createLoanApplication(...) function is a key part of the Tredgate Loan app, enabling users to submit new loan applications.

updateLoanStatus(id: string, status: LoanStatus): Modifying Loan Status

The updateLoanStatus(id: string, status: LoanStatus) function in the Tredgate Loan app is responsible for updating the status of an existing loan application. This function takes the ID of the loan application and the new status as input. It finds the loan application by its ID, updates the status property, and saves the updated array of loans back to localStorage. This function encapsulates the logic for modifying the status of a loan application, ensuring that the changes are persisted and the data remains consistent. The use of the LoanStatus type ensures that the new status is one of the valid values ('pending', 'approved', or 'rejected'). By updating the loan status, the application can reflect the current state of the loan application process. This function is a crucial part of the Tredgate Loan app, allowing users to manage the status of loan applications effectively.

calculateMonthlyPayment(loan: LoanApplication): Loan Payment Calculations

The calculateMonthlyPayment(loan: LoanApplication) function is a key utility in the Tredgate Loan app. It computes the monthly payment for a given loan application based on a simple formula. The formula calculates the total amount to be repaid by adding the interest to the principal amount and then divides the total by the number of months in the term. This function provides a basic estimate of the monthly payment, which is essential for users to understand their financial obligations. While the formula is simplified for demonstration purposes, it provides a reasonable approximation of the monthly payment. The function returns a number representing the monthly payment amount. Rounding (e.g., to two decimals) can be handled in the UI layer to present the payment in a user-friendly format. This function is a crucial part of the Tredgate Loan app, providing users with valuable information about their loan payments.

autoDecideLoan(id: string): Automated Loan Decisions

The autoDecideLoan(id: string) function in the Tredgate Loan app demonstrates a simple automated decision-making process for loan applications. This function takes the ID of a loan application as input and applies a predefined rule to determine whether the loan should be approved or rejected. The rule checks if the loan amount is less than or equal to $100,000 and the term is less than or equal to 60 months. If both conditions are met, the loan status is set to 'approved'; otherwise, it is set to 'rejected'. The updated loan application is then saved to localStorage. This function provides a simplified example of how loan applications can be automatically processed based on predefined criteria. It is designed to be easy to understand and can be used as a starting point for more complex decision-making logic. The autoDecideLoan(id: string) function is a valuable component of the Tredgate Loan app, showcasing how automation can be applied to loan application processing.

Vue Frontend: Building the User Interface

With the business logic in place, the next step in developing the Tredgate Loan app is to build the user interface (UI) using Vue 3. The frontend is structured using a simple Vite + Vue 3 + TypeScript setup, ensuring a modern and efficient development experience. The project structure is organized to promote maintainability and scalability. The core components include App.vue, which serves as the main layout and orchestrates the application's state, LoanForm.vue, which provides the form for creating new loan applications, and LoanList.vue, which displays a list of existing loan applications. Optionally, a LoanSummary.vue component can be created to show loan statistics. Each component is designed to be focused and reusable, adhering to the principles of component-based architecture. The UI is styled using plain CSS, avoiding the complexity of CSS frameworks to keep the application lightweight and simple. Let's explore the details of each component and how they contribute to the overall user experience of the Tredgate Loan app.

Project Structure

The project structure for the Tredgate Loan app is designed to be simple and organized, making it easy to navigate and maintain. The root directory contains essential configuration files such as package.json, tsconfig.json, and vite.config.ts, as well as the index.html entry point. The src directory houses the application's source code, including the main entry point (main.ts), the root component (App.vue), and sub-components like LoanForm.vue and LoanList.vue. The src directory also includes the services directory, which contains the loanService.ts file with the business logic, and the types directory, which contains the loan.ts file defining the domain model. This structure promotes a clear separation of concerns, making it easier to locate and modify specific parts of the application. The use of TypeScript ensures that the code is well-typed and easier to reason about. The project structure is designed to support the KISS principle, keeping the application simple and manageable. By following this structure, developers can easily understand the codebase and contribute to the project.

src/main.ts: Vue App Initialization

The src/main.ts file serves as the entry point for the Vue application in the Tredgate Loan app. This file is responsible for creating the Vue app instance and mounting it to the DOM. It imports the necessary modules from Vue and the root component (App.vue). The createApp function from Vue is used to create a new Vue application instance, and the mount method is used to attach the app to the DOM element with the ID app. This process initializes the Vue application and makes it visible to the user. The src/main.ts file is typically kept minimal, focusing solely on the initialization of the Vue app. This keeps the codebase clean and easy to understand. By creating and mounting the Vue app in src/main.ts, we ensure that the application is properly set up and ready to render the UI. This file is a crucial part of the Tredgate Loan app, as it is the starting point for the entire application.

src/App.vue: Main Layout and State Management

The src/App.vue component is the root component of the Tredgate Loan app. It serves as the main layout for the application and manages the application's state. The layout typically includes the app title (“Tredgate Loan”) and a two-column structure: a form on the left for creating new loans and a list of existing loans on the right. On smaller screens, the layout may adapt to a vertical stacking of the form and list. The App.vue component uses a ref<LoanApplication[]> to hold the list of loans, which is initialized by calling getLoans() on mount. This ensures that the application loads existing loans from localStorage when it starts. When the LoanForm emits a created event or when any action is taken on a loan in the LoanList, the App.vue component reloads the loans from storage using getLoans() to refresh the data. This approach ensures that the UI is always in sync with the data stored in localStorage. The App.vue component orchestrates the state and data flow between the LoanForm and LoanList components, providing a central point of control for the application. This component is a key part of the Tredgate Loan app, as it defines the overall structure and behavior of the application.

src/components/LoanForm.vue: Loan Application Form

The src/components/LoanForm.vue component in the Tredgate Loan app is responsible for rendering the form used to create new loan applications. This component includes form fields for the applicant's name (text), loan amount (number), term in months (number), and interest rate (number). Each field is designed to capture the necessary information for a loan application. When the form is submitted, the component uses the loanService.createLoanApplication function to create a new loan application. It then emits a @created event to its parent component (App.vue), signaling that a new loan has been created and the list needs to be refreshed. The component also includes basic inline validation to ensure that the required fields are filled and the numbers are positive. This validation helps to prevent invalid data from being submitted. The LoanForm.vue component is a crucial part of the Tredgate Loan app, as it provides the interface for users to submit new loan applications. By encapsulating the form logic in a separate component, we keep the code organized and maintainable. This component is designed to be simple and user-friendly, making it easy for users to create new loan applications.

src/components/LoanList.vue: Displaying Loan Applications

The src/components/LoanList.vue component in the Tredgate Loan app is responsible for displaying a list of loan applications. This component takes a loans prop, which is an array of LoanApplication objects. It renders the list as a simple table, with columns for the applicant's name, loan amount, term in months, interest rate, status, and monthly payment. The monthly payment is calculated using the calculateMonthlyPayment function from loanService.ts. The table also includes action buttons for approving, rejecting, and auto-deciding loan applications. These buttons trigger events that are emitted to the parent component (App.vue), allowing it to orchestrate state and refresh the list. The component emits @approve, @reject, and @auto-decide events instead of calling the service directly, ensuring a clear separation of concerns. The LoanList.vue component is a crucial part of the Tredgate Loan app, as it provides the interface for viewing and managing existing loan applications. By encapsulating the list rendering logic in a separate component, we keep the code organized and maintainable. This component is designed to be simple and informative, providing users with a clear overview of their loan applications.

Optional: src/components/LoanSummary.vue: Loan Statistics

An optional component in the Tredgate Loan app is src/components/LoanSummary.vue. This component is designed to display small statistics about the loan applications, such as the number of loans by status and the total amount approved. The goal is to provide a quick overview of the loan portfolio. The component is kept very simple to align with the KISS principle. It can calculate and display statistics based on the loans data, such as the count of pending, approved, and rejected loans, as well as the sum of approved loan amounts. The LoanSummary.vue component enhances the application by providing valuable insights into the loan data. By encapsulating the summary logic in a separate component, we keep the code organized and maintainable. This component is designed to be lightweight and informative, providing users with a clear snapshot of the loan application status.

State Handling in App.vue

State handling in the Tredgate Loan app is primarily managed within the App.vue component. The component uses a ref<LoanApplication[]> to hold the list of loans. This ref is initialized with an empty array when the component is created. On mount, the getLoans() function from loanService.ts is called to load any existing loans from localStorage. The loaded loans are then assigned to the loans ref, making them available for rendering in the LoanList component. When the LoanForm component emits a created event, or when an action is taken on a loan in the LoanList component (e.g., approve, reject, auto-decide), the App.vue component reloads the loans from localStorage using getLoans(). This ensures that the UI is always up-to-date with the latest data. By centralizing state management in App.vue, we simplify the data flow and make it easier to reason about the application's behavior. This approach aligns with the KISS principle, keeping the state management simple and straightforward. The App.vue component serves as the single source of truth for the loan data, ensuring consistency across the application.

Tests: Ensuring Reliability with Vitest

To ensure the reliability and correctness of the business logic in the Tredgate Loan app, unit tests are written using Vitest (or a similar testing framework). These tests are placed in the tests/loanService.test.ts file. The focus of the tests is on the business logic functions in loanService.ts, rather than the Vue components. This ensures that the core logic of the application is thoroughly tested. Tests are added for the calculateMonthlyPayment function, covering a few simple scenarios to verify the calculation logic. Tests are also added for the autoDecideLoan function, ensuring that the automated loan decision rule behaves as expected. The tests are designed to be easy to read and focused on the business logic, making it clear what is being tested and why. By writing unit tests, we can catch potential bugs early in the development process and ensure that the application behaves as expected. Testing is a crucial part of the Tredgate Loan app development, providing confidence in the correctness and stability of the application.

Testing Key Functions

In the Tredgate Loan app, the unit tests focus on validating the behavior of key functions within loanService.ts. For calculateMonthlyPayment, tests should cover various scenarios, including different loan amounts, interest rates, and terms. These tests ensure that the monthly payment is calculated correctly under different conditions. For autoDecideLoan, tests should verify that the loan status is correctly set to 'approved' when the loan amount is less than or equal to $100,000 and the term is less than or equal to 60 months, and to 'rejected' otherwise. These tests ensure that the automated loan decision rule is functioning as expected. By testing these key functions, we can have confidence in the correctness of the core business logic of the application. The tests should be designed to be clear and concise, making it easy to understand what is being tested and why. Testing is a critical part of the Tredgate Loan app development, ensuring that the application behaves reliably and predictably.

GitHub Configuration: Setting Up the Repository

Configuring the GitHub repository for the Tredgate Loan app is essential for setting up continuous integration, defining coding standards, and providing guidance for contributors and GitHub Copilot. This configuration involves adding a .github folder with several key files. The .github/workflows/ci.yml file defines the continuous integration (CI) workflow, which automates the build and test process. The .github/copilot-instructions.md file provides instructions for GitHub Copilot, guiding its behavior within the repository. The .github/ISSUE_TEMPLATE.md file provides a basic issue template, making it easier for contributors to report issues. The .github/PULL_REQUEST_TEMPLATE.md file provides a pull request template, guiding contributors to provide the necessary information when submitting changes. By configuring these files, we can ensure that the repository is well-organized, maintainable, and collaborative. GitHub configuration is a crucial part of the Tredgate Loan app development, setting the stage for a smooth and efficient development process.

Continuous Integration Workflow

The .github/workflows/ci.yml file in the Tredgate Loan app defines the continuous integration (CI) workflow. This workflow automates the process of building and testing the application whenever changes are pushed to the repository. The CI workflow typically includes steps to set up the Node.js environment, install dependencies using npm install, run linting checks using npm run lint (if configured), and run unit tests using npm run test. The workflow is triggered on each push to the repository, ensuring that the application is always in a working state. By automating the build and test process, we can catch potential issues early in the development cycle and ensure that the application remains stable. The CI workflow is a crucial part of the Tredgate Loan app development, providing a safety net for code changes and ensuring the quality of the application.

Copilot Instructions

The .github/copilot-instructions.md file in the Tredgate Loan app provides instructions for GitHub Copilot, guiding its behavior within the repository. These instructions help Copilot understand the project's coding style, architecture, and goals. The instructions typically include guidelines such as preferring small, focused changes, always keeping or adding tests for new business logic, keeping the code simple and readable (KISS principle), and avoiding external backends or databases. By providing these instructions, we can ensure that Copilot's suggestions align with the project's requirements and maintainability goals. The Copilot instructions are a valuable tool for guiding AI-assisted development, helping to ensure that the generated code is consistent with the project's overall design and quality standards. This file is a key part of the Tredgate Loan app development, ensuring that Copilot is used effectively and contributes positively to the project.

Issue and Pull Request Templates

The .github/ISSUE_TEMPLATE.md and .github/PULL_REQUEST_TEMPLATE.md files in the Tredgate Loan app provide templates for creating issues and pull requests, respectively. The issue template typically includes sections for describing the context, problem, and proposed solution. This helps contributors provide the necessary information when reporting issues, making it easier for maintainers to understand and address them. The pull request template typically includes sections for summarizing the changes, listing the changes made, providing instructions on how to test the changes, and identifying any potential risks. This helps contributors provide a clear and comprehensive overview of their changes, making it easier for maintainers to review and merge them. By providing these templates, we can ensure that issues and pull requests are well-documented and easy to understand, contributing to a more efficient and collaborative development process. These templates are a valuable part of the Tredgate Loan app development, promoting clear communication and collaboration within the project.

package.json Scripts: Streamlining Development Tasks

The package.json file in the Tredgate Loan app includes scripts that streamline common development tasks. These scripts are defined in the scripts section of the file and can be executed using npm run <script-name>. Essential scripts include `