I have some experience using both libraries, so I'll try my best to explain them:

Intl.NumberFormat and decimal.jsare libraries in JavaScript for formatting and manipulating numbers. However, while they are similar in some ways, they are very different in others.

Intl.NumberFormat is a built-in JavaScript library that provides localized support for number formatting, including decimal and grouping separators, decimal precision, and currency formatting. It is widely used to format numbers according to the user's language and region.

Decimal.js is a third-party library that provides arbitrary-precision decimal arithmetic for JavaScript. It allows precise calculations using decimal numbers, which is often required in financial and scientific applications where rounding errors can have significant effects.

Although Intl.NumberFormat can handle basic currency formatting, it may not be suitable for all use cases. For example, it may not be able to handle more complex currency formatting requirements, such as rounding rules or the use of multiple currencies in the same document. In this case, decimal.js can provide more precise and flexible currency handling capabilities.

Hope this answers your question!