Why care at all?¶
Typescript is a superset of Javascript that is ultimately compiled back to Javascript. Typescript isn't consumed natively. The big benefit that we get from using Typescript is the benefit of type-checking. All sorts of problems can occur when we aren't absolutely certain of the types we are using, and by using Typescript to enforce types, we can catch these problems before they become a problem.
Types¶
Primitive types.
- number
- string
- boolean
- void
- undefined
- null
Object types.
- Array
- Function
- Classes
- Objects
Type Annotations¶
Type Inference¶
The Typescript compiler is able to determine a type when the code clearly gives it away. This is possible when a variable declaration and initialization are on the same line. For example:
const message = 'hello'; - Typescript can infer that message is a string.
const message = 10; - Typescript can infer that message is a number.
We should always use type inference when we can, but there will be times that the type can't be inferred.
- declaring a variable and initializing it later.
- when the variable will be of a type that can't be inferred.
- when the return value is of 'any' type and we need to specify a type.
Any Type¶
Functions¶
- arguments
- return types
- anonymous functions
Never Type¶
Unsorted¶
Bang Symbol¶
The bang symbol at the end of a variable indicates that the variable will not be null or undefined. This is a way to tell Typescript that we are sure that the variable will have a value. This is from the developers point of view, and if the variable is null or undefined, then the program will throw an error. You would still need to handle it if you need gracefully handle the error.
let message: string | null = null;
let messageLength = message!.length;
Return Type¶
We can specify the return type of a function by using a colon after the arguments and specifying the type. If the function doesn't return anything, then we can use the void type.
function add(a: number, b: number): number {
return a + b;
}