4IT580: DocsTypeScript cheatsheet
TypeScript builds on top of JavaScript. First, you write the TypeScript code. Then, you compile the TypeScript code into plain JavaScript code using a TypeScript compiler.
Once you have the plain JavaScript code, you can deploy it to any environment that JavaScript runs.
Why TypeScript?
- It reduces many common code bugs during development
- Code readability - predictability
- Easier to maintain in long term
Primitives
string
number
boolean
Literal value
Structural types
Specific object with properties
Type aliases
Array
Using primitives
Using structural types
Tuple
Enum
DO NOT USE ! There are many problems with TypeScript enums. It is a crime against humanity to use in TypeScript.
Instead use string union:
For more info see this video.
Optional and nullable
Optional value
This is usefull for optional properties.
Nullable
This is usefull to express that value is specail state.
Functions
Parameters
ES6 arrow function
Return type
Optional parameters
Default parameters
Rest parameter
Structural typing
Sometimes called "duck typing" (If it walks like a duck and it quacks like a duck, then it must be a duck).
Comparing types is done by comparing the structures, not the names of types.
If contains the same properties as , it is safe to pass it as an argument of .
You can read about structural type system in official docs.
Interfaces
Basic
Extending interface
Shall I use or for objects?
Watch this video for explanation. TL;DR: use .
Unions and Intersection
Union - OR
String literal
Intersection - AND
Generics
Basic
Constraints
Miscellaneous
Type
When you want to assign whatever type, you can use . Good practice is to NOT use this type, since you lose the typesafety.
Type
This type is usually used with casting or as a default type in generics.
Type
Casting type
Please try to avoid type casting. In some advanced use-cases there is no way around it, but it should be avoided as much as possible.
Inference
Most of the type, when you create a new variable you dont have to specify the type, since TypeScript can infer it for you. It is always good to check, if the inferred type is correct, in your IDE.
Utilities
Pick
more props