Validate EU and International VAT Numbers Validate VAT identification numbers for European and international formats.

The tool uses a combination of regular expressions and data structures to validate VAT numbers. It employs an object called VAT_FORMATS, which stores the patterns for each country's VAT format as key-value pairs, with the country code serving as the key. For example, the pattern for Austria is defined as /^ATU\d{8}$/, indicating that a valid Austrian VAT number must start with "ATU" followed by 8 digits. When a user inputs a VAT number, it is cleaned and uppercased using JavaScript's replace() method to remove any whitespace or special characters.

The tool then attempts to detect the country of origin based on the prefix of the input string, handling special cases such as Switzerland's "CHE" and Greece's "EL" prefixes. It checks if the cleaned input matches the expected pattern for the detected country using the test() method of the RegExp object stored in VAT_FORMATS. If a match is found, it returns an object with a valid property set to true and details about the validation process, including the country name, expected format, and whether the input matches that format.

The user interface is built using React, which manages state changes and updates the UI accordingly. When the user clicks the "Validate" button or presses Enter, it triggers the handleValidate function, which calls the validateVat function with the current input as an argument. This function uses JavaScript's callback functionality to ensure that the result of the validation is updated in the component's state.

The tool also utilizes React's useState and useCallback hooks to manage its state and optimize performance by memoizing the handleValidate function. The details of the validation process are displayed below the input field, providing users with immediate feedback on whether their VAT number is valid or not, along with specific information about what was checked during the validation process.

The validateVat function itself uses a simple yet effective approach to validate VAT numbers by checking for empty strings, strings that are too short, and then testing the cleaned string against the pattern defined for the detected country. This combination of data structures, regular expressions, and React's state management capabilities enables it to efficiently validate VAT numbers from over 30 countries with high accuracy.

It is worth noting that this implementation relies on the ECMAScript 2015+ syntax, specifically using const declarations for variables like VAT_FORMATS and utilizing arrow functions for concise function definitions. Additionally, the tool uses TypeScript type annotations to define interfaces such as VatResult, ensuring clarity about the structure of data exchanged within the application.

The use of specific technologies such as React's useState hook allows for efficient management of component state, while the regular expression patterns stored in VAT_FORMATS enable precise matching against country-specific VAT formats. This implementation demonstrates a clear understanding of how to leverage JavaScript and its ecosystem to build effective tools for tasks like VAT number validation.