how to define and use static variable in typescript

Question

I want to define a static variable called index in my function, which does such as index++. that means that if this method is called, the varaible will be added.

Answer 1

Typescript is just JavaScript with types, JavaScript does not have any such static function variables, so neither does Typescript.

You can use a variable defined in the parent context (such as the module context) to get something akin to what you want:

let index = 0;
function fn() {
  index++
}

fn()
console.log(index); // 1

fn()
console.log(index); // 2

Playground Link

Answer 2

We can use static variables in Typescript.

class Test {
    static index = 1;

    static print() {
        console.log(Test.index++);
    }
}
Test.print(); // prints 1
Test.print(); // prints 2