Static variables in JavaScript

Question

How can I create static variables in Javascript?

Answer 1

I use static function variables a lot and it's a real shame JS doesn't have a built-in mechanism for that. Too often I see code where variables and functions are defined in an outer scope even though they're just used inside one function. This is ugly, error prone and just asking for trouble...

I came up with the following method:

if (typeof Function.prototype.statics === 'undefined') {
  Function.prototype.statics = function(init) {
    if (!this._statics) this._statics = init ? init() : {};
    return this._statics;
  }
}

This adds a 'statics' method to all functions (yes, just relax about it), when called it will add an empty object (_statics) to the function object and return it. If an init function is supplied _statics will be set to init() result.

You can then do:

function f() {
  const _s = f.statics(() => ({ v1=3, v2=somefunc() });

  if (_s.v1==3) { ++_s.v1; _s.v2(_s.v1); }
} 

Comparing this to an IIFE which is the other correct answer, this has the disadvantage of adding one assignment and one if on every function call and adding a '_statics' member to the function, however there are a few advantages: the arguments are there at the top not in the internal function, using a 'static' in the internal function code is explicit with an '_s.' prefix, and it is overall simpler to look at and understand.