Well its been a while since I last used JavaScript, but I’m back at it with a bang. However, it would appear that people are still writing JavaScript as awful as ever. I’m not claiming to be a JavaScript expert but I see people do things in JavaScript that they wouldn’t even consider doing in languages like C++, C#, Java, and so on. Why is this the case? I can only presume that they don’t know any better. With this in mind, let’s take look a few not so nice bits of JavaScript namely global variables and scope, and see how we can make this situation better.
With C (and C++) we have global variables, that is, a variable which is available at each and every scope of your program. Why is this bad? Well due to the fact that this variable does not have any sense of locality, it can be changed anywhere in your code. Thus, there can be a large number of dependencies on such a variable – something which all good developers know is bad. This can also lead to name clashes resulting in unpredictable behaviour. So why is JavaScript so bad? Well it bases its programming model on global variables. Damn.
So what are the problems with scope in JavaScript? Well JavaScript does not have block scope – this may appear odd to those used to C-style syntax. What does this actually mean and what’s the problem with this? Well I’ll steal an example from the book Javascript – The Good Bits by Douglas Crockford where you can see how confusing this can be:
var foo = function () {
var a = 3, b = 5;
var bar = function () {
var b = 7, c = 11;
// At this point, a is 3, b is 7, and c is 11
a += b + c;
// At this point, a is 21, b is 7, and c is 11
};
// At this point, a is 3, b is 5, and c is not defined
bar();
// At this point, a is 21, b is 5
};
However, despite these nuances in the JavaScript language, with a little thought and engineering we can get round this.
First, let me say that JavaScript really is a great language, don’t underestimate it. Many languages have bad features, it does not mean that you have to use them.
Now getting round the global variable problem is pretty simple, we create a global object and place all our JavaScript code within this object. The code below shows an example of how to do this.
var APPLICATION_NAMESPACE = {};
APPLICATION_NAMESPACE.my_object = {
my_name : "Name",
my_function : function () { alert("ALERT"); }
}
This style of coding in JavaScript should be familiar to users of jQuery – instead of APPLICATION_NAMESPACE you use $ or jQuery. There we have it, this gives us a nice way to get round those pesky global variables.
Now, if like me, you are used to a more object-oriented (OO) style of software development then JavaScript can appear a little awkward at first. With no classes and traditional inheritance the typical OO developer is left wondering what to do. This need not be the case.
One development pattern that comes to the rescue for OO developers has been proposed, once again, by Douglas Crockford and is known as the module pattern. So how can we use it? Well say we want to create a “class” Person that has a “public” method fullname which uses a “private” method concat, this is represented using the module pattern as follows:
function Person () {
function concat() {
return firstname + surname;
}
return {
fullname: function(firstname, surname) {
return concat(firstname, surname);
}
}
}
// To use Person we do the following
var person = new Person();
var name = person.fullname("Davie", "Jones");
As you can see this allows for sensible scoping of variables and functions, and at the same time makes a JavaScript objects look like classes. Also, this method of developing objects in JavaScript just about eliminates the need for global objects.
I’m a little hesitant to use JavaScript as a fully blown OO language – as this is not how it was intended. Instead we should embrace the alternative style of programming that JavaScript gives us. After all, if you were using a functional language like Haskell, F#, Scala and so on, you wouldn’t expect to write code as you would in a language that supports the typical OO constructs.
The fact is that JavaScript is here to stay for a long long time, so you may as well learn to love it 😀 .
