TypeScript static classes

Question

I wanted to move to TypeScript from traditional JS because I like the C#-like syntax. My problem is that I can\'t find out how to declare static classes in TypeScript.

Answer 1

See http://www.basarat.com/2013/04/typescript-static-constructors-for.html

This is a way to 'fake' a static constructor. It's not without its dangers - see the referenced codeplex item.

class Test {
    static foo = "orig";

    // Non void static function
    static stat() {
        console.log("Do any static construction here");
        foo = "static initialized";
        // Required to make function non void
        return null;
    }
    // Static variable assignment
    static statrun = Test.stat();
}

// Static construction will have been done:
console.log(Test.foo);

Answer 2

One possible way to achieve this is to have static instances of a class within another class. For example:

class SystemParams
{
  pageWidth:  number = 8270;
  pageHeight: number = 11690;  
}

class DocLevelParams
{
  totalPages: number = 0;
}

class Wrapper
{ 
  static System: SystemParams = new SystemParams();
  static DocLevel: DocLevelParams = new DocLevelParams();
}

Then parameters can be accessed using Wrapper, without having to declare an instance of it. For example:

Wrapper.System.pageWidth = 1234;
Wrapper.DocLevel.totalPages = 10;

So you get the benefits of the JavaScript type object (as described in the original question) but with the benefits of being able to add the TypeScript typing. Additionally, it avoids having to add 'static' in front of all the parameters in the class.

Answer 3

Static classes in languages like C# exist because there are no other top-level constructs to group data and functions. In JavaScript, however, they do and so it is much more natural to just declare an object like you did. To more closely mimick the class syntax, you can declare methods like so:

const myStaticClass = {
    property: 10,

    method() {

    }
}

Answer 4

Abstract classes have been a first-class citizen of TypeScript since TypeScript 1.6. You cannot instantiate an abstract class.

Here is an example:

export abstract class MyClass {         
    public static myProp = "Hello";

    public static doSomething(): string {
      return "World";
    }
}

const okay = MyClass.doSomething();

//const errors = new MyClass(); // Error

Answer 5

You can also use keyword namespace to organize your variables, classes, methods and so on. See doc

namespace Validation {
    export interface StringValidator {
        isAcceptable(s: string): boolean;
    }

    const lettersRegexp = /^[A-Za-z]+$/;
    const numberRegexp = /^[0-9]+$/;

    export class LettersOnlyValidator implements StringValidator {
        isAcceptable(s: string) {
            return lettersRegexp.test(s);
        }
    }

    export class ZipCodeValidator implements StringValidator {
        isAcceptable(s: string) {
            return s.length === 5 && numberRegexp.test(s);
        }
    }
}

Answer 6

This question is quite dated yet I wanted to leave an answer that leverages the current version of the language. Unfortunately static classes still don't exist in TypeScript however you can write a class that behaves similar with only a small overhead using a private constructor which prevents instantiation of classes from outside.

class MyStaticClass {
    public static readonly property: number = 42;
    public static myMethod(): void { /* ... */ }
    private constructor() { /* noop */ }
}

This snippet will allow you to use "static" classes similar to the C# counterpart with the only downside that it is still possible to instantiate them from inside. Fortunately though you cannot extend classes with private constructors.