How to determine if a function has been called without setting global variable

Question

I am looking for a good technique to get away from what I am tempted to do: to set a global variable.

The first time someone runs a function by clicking a button it

Answer 1

While @Levi's answer ought to work just fine, I would like to present another option. You would over write the init function to do nothing once it has been called.

var init = function () {
   // do the initializing

    init = function() {
        return false;
    }
};

The function when called the first time will do the init. It will then immediately overwrite itself to return false the next time its called. The second time the function is called, the function body will only contain return false.

For more reading: http://www.ericfeminella.com/blog/2011/11/19/function-overwriting-in-javascript/

Answer 2

Why don't you just check to see if your draggables have a class of draggable on them?

if ($('.mydiv').is('.draggable')) {
     //do something
}

Answer 3

You could add a property to the function:

function init() {
    init.called = true;
}

init();

if(init.called) {
    //stuff
}

Answer 4

Function.prototype.fired = false;

function myfunc() { 
    myfunc.fired = true; 
    // your stuff
};

console.log(myfunc.fired) // false

myfunc();

console.log(myfunc.fired) // true

Answer 5

What you could do is unhook the init function from the prototype.

​var Obj = function () {
    this.init = function () {
        document.write("init called<br/>");
        this.init = null;
    }
}
var o = new Obj();
if (o.init) document.write("exists!<br/>");
o.init();
if (o.init) document.write("exists!<br/>");
o.init();

​ The first if will be true and print exists! but since the function removes itself, the second if will fail. In my example, I call the second init unconditionally just to show that nothing will happen, but of course you could call it only if it exists:

if (o.init) o.init();

http://jsfiddle.net/coreyog/Wd3Q2/

Answer 6

The correct approach is to use the Javascript Proxy APIs to trap the function calls using apply handler.

const initFun = (args) => {
  console.log('args', args);
}
const init = new Proxy(initFun, {
  apply(target, thisArg, args){
    target.calls = target.calls ? target.calls + 1 : 1;
    return target.apply(thisArg, args);
  }
});

init('hi');
console.log(init.calls); // 1
init('hello');
console.log(init.calls); // 2