Arrays let you store and manage ordered collections of data. In TypeScript, arrays are type-safe, which means you define what type of elements an array can hold. This helps you catch errors early and makes your code more predictable. You declare an array type in two main ways: by adding square brackets to a type, like number[], or by using the generic Array<number> syntax. Both forms mean the same thing—a list where every element is a number. You can do the same with other types, such as string[] or Array<string>, to create arrays of strings.

Sometimes, you want to make sure an array cannot be changed after it's created. TypeScript provides the readonly modifier for this purpose. A readonly array means you cannot add, remove, or modify its elements. You declare a readonly array using readonly number[] or ReadonlyArray<number>. This is useful when you want to prevent accidental changes to data that should stay constant. As a best practice, always specify the element type when declaring an array, and use readonly if you want to guarantee immutability. This makes your code safer and easier to maintain.