1. All JavaScript codes are valid Typescript codes. Use the TypeScript compiler to compile the Javascript code in TypeScript. The compiled result is exactly the same as the original Javascript code, that is, the file extension is changed from .js to .ts, which will not cause any negative impact
2. Migrate JavaScript code to TypeScript. TypeScript will perform type checking on the code and will receive some error messages. Using any can solve most of the error reporting problems
3. Type annotations Add
type annotations to function parameters, and add constraints to functions or variables. In the example, the greeter function is expected to receive a field string parameter. If the parameter is changed to an array, an error message will be generated after
recompilation .
4. Underfined and null
5. Array, there are two ways to define an array.
Connect [] after the original type
to use array generics, Array<element type>
The Tuple
tuple type allows to represent an array with a known number and type of elements, and the types of each element do not have to be the same
Enum enum
is a supplement to Javascript standard data types
Any
does not want the type checker to check the value but let them pass the check of the compilation stage directly, and mark these variables with any type
void
In a way, the void type is like the opposite of any type, it means that there is no type. When a function does not return a value, you usually see that its return type is void
object
object represents a non-primitive type, that is, a type other than number, string, and boolean.
Union type
Union types (Union Types) indicate that the value can be one of multiple types
Type assertion
No special data checking and deconstruction
Angle bracket syntax, as syntax
Type inference
Type inference: TS will infer a type when there is no clear specified type.
There are the following two situations: 1. When a variable is assigned a value, it is inferred to be the corresponding type. 2. When the variable is not assigned a value, it is inferred to be any type
