CODEWITHSUNDEEP
javascriptoopobjectmethodsproperties
pixo-drone
pixo-drone

Reputation: 83

Some questions about OOP

I have an object called clock.

I have a method of said object called time.

If I used this.propertyName inside my time method, this will give the property to my clock object, right? But what if there is an if/else statement (within the time method itself), for example, which needs to run before the value of the property can be assigned?

if(t.getHours() >= 12){
        this.ap = "AM";
    }else{
        this.ap = "PM";
    }

So, if I used a simple value like this.ap = "hi", this works fine. It gives the property to my object. If I have a statement like shown above, the property is undefined. What is the best way around this?

Also, another quick question since I'm only just starting to use my own objects. If I have an object with 3 separate methods, and I want to use a value in ALL methods that's been declared within 1 method, assigning it as a property of my object allows me to do this. Am I right?

So If I used var property = "" in one method, the only way to access this in my other methods is to return it. But setting the property to the object solves this? I realize I can experiment around with this but I'd rather just know the proper way.

Edit: Here's an example. Obviously I'm misunderstanding something. I can't seem to define properties from within a method.

var clock = {};

clock.test1 = "test 1.";

clock.time = function(){

    clock.test = "test 2."; 

    if(t.getHours() >= 12){
        clock.ap = "PM";
    }else{
        clock.ap = "AM";
    }

}

alert(clock.test1);  //success
alert(clock.test); //returns undefined
    alert(clock.ap);  //returns undefined

Upvotes: -1

Views: 48

Answers (1)

Matt Burland
Matt Burland

Reputation: 45145

The usual way to avoid problems with binding this is to do something like this:

var MyObject = function() {
    var self = this;
    self.someProperty = "foo";

    self.someMethod() {
        self.someProperty = "bar";
    }
}

var anInstance = new MyObject();
console.log(anInstance.someProperty);      // foo
anInstance.someMethod();
console.log(anInstance.someProperty);      // bar

This avoids problems with this being something other than what you expected it to be, which can happen depending on how you call methods (using a method as a handler for some DOM event for example).

This example works by exploiting closure, which is a very important concept in Javascript that you should read up on (Google it).

Upvotes: 2

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