Type annotations
One of the most commonly used features of TypeScript is its type annotations, where variables are annotated with the data type of the information they contain.
const pi: number = 3.1415926535
let found: boolean = false
By adding type annotations, TypeScript can use type inference to detect a wide variety of situations where a valid JavaScript program would encounter runtime errors.
Notice that even without type annotations, TypeScript will use type inference to determine the data types of variables and functions.
There is also a special type any which can be applied to a variable whose data type is unknown. This means TypeScript
will be unable to detect an error in the same program as above, but the program will produce a runtime error when it is executed.
TypeScript helps you prevent runtime errors by exposing a wide range of potential issues as compilation errors, which can be addressed during the development process rather than as a bug fix later on.