Now we've already looked at JavaScript arrays in a previous lesson, and we've discussed how we can annotate it using the array class name, passing in the generic argument. Now, arrays appear quite heavily within JavaScript code, so TypeScript provides a nice shorthand syntax for declaring arrays where you simply put in the type of the members of the array, followed by the square brackets. Now, arrays can be of any length. You can have an array of one item or an array of five items. However, all items of the array must match the type

that is used in the type annotation. Here we have an array of numbers, so if we try to assign an array of strings to this variable, we will get a compiled time error from TypeScript. Now, sometimes you want to declare an array of a fixed length. An example of that is an array with two numbers, which can be used to represent a point in space. A fixed length array is commonly called a topple in programming jargon and TypeScript support declaring couples within its type system. Here we've declared a couple of two members, and both of these members must be of type number.

We can use this to represent a point in space in terms of usage. We can assign any array of two numbers to this variable. If you try to assign an array which has less than two items or more than two items, we will get a compiled time error from TypeScript. Also, the members of the array need to match the type annotation here. If you said that both members of the array must be of type number, so if you try to assign an array that has a string in there, you will get a compile time error from TypeScript.