call conditional method from constructor

Question

I'm trying to do something really simple but not able to achieve this.

var Dummy = function() {
    self = this;
    setTimeout(function() {

        if(self.render) {
            self.render(); 
        }
    }, 10);
};
var test = new Dummy();
test.render = function() {
    console.log('Make constructor call this method? ');   
}

How can I make this work without settimeout?

Goal: Based on the function names attached to instance, I want to call them in particular order.

eg:

var Dummy = function() {
    if(function1) {
       function1();
    }
    if(function2) {
       function2();
    }
};

You cannot call something that does not exist. What is the *actual* problem you are trying to solve? — Felix Kling, Jul 14 '15 at 20:04
Again, you cannot call something that does not exist. Again, *why* are you trying to do this? *What* is it really that you are trying to do? — Felix Kling, Jul 14 '15 at 20:06
Achieve what? Maybe pass the render function as an argument to the constructor? — Matt Burland, Jul 14 '15 at 20:06
Unless you explicitly say what you want to achieve nobody will be able to help you, mainly because your code makes no sense. — Daniel Conde Marin, Jul 14 '15 at 20:07
It makes perfect sense to me, and unless I'm missing something it works when I try it. @JS-JMS-WEB you should probably define the `test.render` function before you create the new `Dummy` object though, to avoid a race condition. — John Wiseman, Jul 14 '15 at 20:09
And what does "Based on the function attached to instance" mean? — Felix Kling, Jul 14 '15 at 20:10

Matt Burland · Answer 1 · 2015-07-14T20:18:41.877

You question isn't entirely clear, but I assume you have a function that you want to have called as soon as your object has been instantiated. The simplest way to do this is to pass the function as an argument.

Something like:

var Dummy = function(myFunction) {
    self = this;
    self.render = myFunction;     // if you want to be able to call it again later
    self.render();                // if you want to call it now
};

var test = new Dummy(function() {
    console.log('Make constructor call this method? ');   
});

var anotherTest = new Dummy(function() {
    console.log("this instance will have a different render function");
});

Now, of course, this can be extended to handle any number of functions passed in:

var Dummy = function(func1, func2) {
   // Note: you may want to check the arguments actually are functions
   if (func1) {
       func1();
   }
   if (func2) {
       func2();
   }
}

var test = new Dummy(function() { console.log("1"); },
    function() { console.log("2"); });

Or you could pass in an array of functions in the order you want them executed:

var Dummy = function(funcArray) {
    for (var i=0; i < funcArray.length; i++) {
        funcArray[i]();
    }
}

var test = new Dummy([function() { console.log("1"); },
    function() { console.log("2"); }]);

Or you could pass in an object with the functions (and names) you want:

var Dummy = function(funcObject) {
    if (funcObject.func1) {
        funcObject.func1();
    }
    if (funcObject.func2) {
        funcObject.func2();
    }
}

var test = new Dummy({ func1 : function() { console.log("1"); },
    func2: function() { console.log("2"); });

Like the idea of passing object. That's how backbone does it! — JS-JMS-WEB, Jul 14 '15 at 20:21

score 2 · Accepted Answer · answered Jul 14 '15 at 20:16

I am not sure what you are trying to do, but if what you want to do is call multiple functions (in order) when you instantiate an object instance of Dummy:

var Dummy = function() {
     for (var i = 0; i < arguments.length; i++) {
        if (typeof arguments[i] === "function") {
             arguments[i]();
        }
     }
}

var function1 = function() { console.log('Func 1 executed!'); }
var function2 = function() { console.log('Func 2 executed!'); }

var d = new Dummy(func1, func2, 'maybe a string also');

// log
'Func1 executed!'
'Func2 executed!'

Exactly what I wanted to do! Couldn't explain it properly I guess. Thanks — JS-JMS-WEB, Jul 14 '15 at 20:18

score 0 · Answer 3 · answered Jul 14 '15 at 20:06

Becuase you are adding render() method on the Dummy instance (test) and you are not even calling that render() method.

I think you need to change to the following (assuming you don't want to use prototype to create the render() method):

var Dummy = function() {

    this.render = function() {
        console.log('Make constructor call this method called? ');   
    };

    self = this;

    setTimeout(function() {
        console.log(self);
        self.render(); 
    }, 10);
};
var test = new Dummy();

call conditional method from constructor

3 Answers3