Stateful Functions

A common feature in other programming languages is usage of the static keyword to increase the lifetime (not scope) of a function variable to live beyond function invocations. Here is a C sample that achieves this:

void called() {
static count = 0;
count++;
printf("Called : %d", count);
}
int main () {
called(); // Called : 1
called(); // Called : 2
return 0;
}

Since JavaScript (or TypeScript) doesn't have function statics you can achieve the same thing using various abstractions that wrap over a local variable e.g. using a class :

const {called} = new class {
count = 0;
called = () => {
this.count++;
console.log(`Called : ${this.count}`);
}
};
called(); // Called : 1
called(); // Called : 2

C++ developers also try and achieve this using a pattern they call functor (a class that overrides the operator ()).