function Animal(type) {
var data = [];
data['type'] = type;
this.getType = function () {
return data['type'];
}
}
var fluffy = new Animal('dog');
fluffy.getType(); // returns 'dog'
In this example, I create a local array called data within the Animal class. When an Animal object is instantiated, a value for type is passed and set in the data array. This value can't be overwritten as it's private (the Animal function defines its scope). The only way to read the type value once an object is instantiated is to call the getType method that I've explicitly exposed. Since getType is defined inside Animal, it has access to data by virtue of the closure created by Animal. This way, people can read the object's type but not change it.
It's important to note that the "read-only" technique will not work when an object is inherited from. Every object instantiated after the inheritance is performed will share those read-only variables and overwrite each other's values. The simplest solution is to convert the read-only variables in the class to public ones. If however, you must keep them private, you can employ the technique pointed out by Philippe in the comments.
Public
There are times however, that you'll want to be able to read and write a property's value at will. To do that, you need to expose the property using the this operator.
复制代码 代码如下:
function Animal() {
this.mood = '';
}
var fluffy = new Animal();
fluffy.mood = 'happy';
fluffy.mood; // returns 'happy'
This time our Animal class exposes a property named mood which can be written to and read at will. You can equally assign a function to public properties like the getType function in the previous example. Just be careful not to assign a value to a property like getType or you'll destroy it with your value.
Completely Private
Finally, you might find yourself in scenarios where you need a local variable that's completely private. In this case, you can use the same pattern as the first example and just not create a public method for people to access it.
复制代码 代码如下:
function Animal() {
var secret = "You'll never know!"
}
var fluffy = new Animal();
Writing a Flexible API
Now that we've covered class creation, we need to future proof them in order to keep up with product requirement changes. If you've done any project work, or maintained a product long-term, you know that requirements change. It's a fact of life. To think otherwise is to doom your code to obsolescence before it's even written. You may suddenly have to animate your tab content, or have it fetch data via an Ajax call. Though it's impossible to truly predict the future, it is possible to write code that's flexible enough to be reasonably future proof.
Saner Parameter Lists
One place where future-proofing can be done is when designing parameter lists. They're the main point of contact for people implementing your code and can be problematic if not well designed. What you want to avoid are parameter lists like this:
复制代码 代码如下: