"Can I use separate JS files or the Module pattern?"
Answer: Use the Instance pattern.
There are only 2 ways to get JavaScript into HTML:
1. Inline - <script> some JavaScript </script>
2. Link - <script src='main.js'></script>
I know this is obvious but we need that common ground for what comes next. ;)
JavaScript does not have the ability to "import" other JavaScript files into it's self. All the "importing" is done in the HTML. You can do this several ways:
- Link each one individually into the HMTL
- Dynamically link them in through some JavaScript
var script = document.createElement("script");
script.src = "all.js";
document.documentElement.firstChild.appendChild(script);It is import to consider reasons for separating JavaScript into separate files.
- Maintainability - it becomes easier to work on one piece at a time
- Readability - if everything is in one big file it is very hard to see what is what
- Division of Labor - it is easier to have multiple developers working on multiple files instead of one big one
- Reuse - all your functions can be broken up into highly cohesive modules
Separate JavaScript files DO NOT make things Private, Closures make things Private.
Now, consider at the end of the day when everything is ready for production the best thing you could do is Optimize your JavaScript by combining it all into one file so that the user only has one file to download.
When dealing with Private variables in JavaScript, you will at some point want to access them.
- Public function - can be altered.
- Privileged function - a Public function that can access the Private variable.
- However if the function is in an Instance then it can only be altered in each Object.
Let me illustrate with some code.
main.js
var MODULE = (function () {
//Private variables
var privateParent,
app;
privateParent = 'parentPrivate';
return app = {
//Privileged method
getPrivateParent: function() {
return privateParent;
}
};
}());
MODULE.sub = (function (parentApp) {
//Private variables
var childMessage,
Constr;
childMessage = ' - trying to access parent private field: ' + parentApp.getPrivateParent(); //prints parentPrivate
Constr = function () {
this.childF = this.childFunction();
};
//Constructor
Constr.prototype = {
constructor: MODULE.sub,
version: "1.0",
childFunction: function () {
$("#testing-div").append(childMessage + "");
}
};
return Constr;
}(MODULE));
//We could just as easily print to the console, but the 'append' allows us to display the results on the page.
$("#testing-div").append("This first part shows what does not work; everything is 'undefined'. " + "");
$("#testing-div").append("You are unable to access the var or func directly. " + "");
$("#testing-div").append("MODULE.privateParent = " + MODULE.privateParent + "");
$("#testing-div").append("MODULE.app = " + MODULE.app + "");
$("#testing-div").append("MODULE.sub.childMessage = " + MODULE.sub.childMessage + "");
$("#testing-div").append("MODULE.sub.Constr = " + MODULE.sub.Constr + "");
$("#testing-div").append("MODULE.sub.childFunction = " + MODULE.sub.childFunction + "");
$("#testing-div").append("END lesson. You must access childFunction() through the new operator." + "");
$("#testing-div").append("----------------------------------------------------" + "");
$("#testing-div").append("Let's see if making an instance of the Object works" + "");
var test = new MODULE.sub();
test.childFunction(); //run the method
$("#testing-div").append("Looks like it did!!!!" + "");
$("#testing-div").append("----------------------------------------------------" + "");
$("#testing-div").append("Now let's try to change the childFunction() ?" + "");
test.childFunction = function() {$("#testing-div").append(" - This is a new function." + "");}
test.childFunction(); // altered version
$("#testing-div").append("Looks like it was changed. :(" + "");
$("#testing-div").append("----------------------------------------------------" + "");
$("#testing-div").append("Does it stay changed?" + "");
var test2 = new MODULE.sub();
test2.childFunction(); // doesn't work
$("#testing-div").append("NO, it was only Overriden in the 'test' Object. It did not effect all the other new objects. :)" + "");
$("#testing-div").append("----------------------------------------------------" + "");module-test.html
<html>
<head>
<meta charset="ISO-8859-1">
<title>Module Test</title>
</head>
<body>
<h1>This is a test for separate Modules and Private variables.</h1>
<div id="testing-div">
</div>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="main.js"></script>
</body>
</html>This is what is displayed on the web page after you run the above code.
This is a test for separate Modules and Private variables.
This first part shows what does not work; everything is 'undefined'.
You are unable to access the var or func directly.
MODULE.privateParent = undefined
MODULE.app = undefined
MODULE.sub.childMessage = undefined
MODULE.sub.Constr = undefined
MODULE.sub.childFunction = undefined
END lesson. You must access childFunction() through the new operator.
----------------------------------------------------
Let's see if making an instance of the Object works
- trying to access parent private field: parentPrivate
- trying to access parent private field: parentPrivate
Looks like it did!!!!
----------------------------------------------------
Now let's try to change the childFunction() ?
- This is a new function.
Looks like it was changed. :(
----------------------------------------------------
Does it stay changed?
- trying to access parent private field: parentPrivate
- trying to access parent private field: parentPrivate
NO, it was only Overriden in the 'test' Object. It did not effect all the other new objects. :)
----------------------------------------------------
This is a test for separate Modules and Private variables.
This first part shows what does not work; everything is 'undefined'.
You are unable to access the var or func directly.
MODULE.privateParent = undefined
MODULE.app = undefined
MODULE.sub.childMessage = undefined
MODULE.sub.Constr = undefined
MODULE.sub.childFunction = undefined
END lesson. You must access childFunction() through the new operator.
----------------------------------------------------
Let's see if making an instance of the Object works
- trying to access parent private field: parentPrivate
- trying to access parent private field: parentPrivate
Looks like it did!!!!
----------------------------------------------------
Now let's try to change the childFunction() ?
- This is a new function.
Looks like it was changed. :(
----------------------------------------------------
Does it stay changed?
- trying to access parent private field: parentPrivate
- trying to access parent private field: parentPrivate
NO, it was only Overriden in the 'test' Object. It did not effect all the other new objects. :)
----------------------------------------------------If you want to use RequireJS to accomplish the above, you can. RequireJS uses the Module Pattern which is what you and I are already using. If you want to separate out the files then there are two ways to do this.
1. Normal - Just set up your JS files to use RequireJS and drop in the above Modules with only a slight modification.
2. Leveraged - Use the Module nature of RequireJS as the modules to set up the closures. This looks like it may be harder to figure out but it may be more efficient in the long run.
NOTE: I haven't had a chance to compare these two options yet but wanted to include them for completeness.
You may also find the following references helpful:
- JavaScript Module Pattern: In-Depth
- Private Members in JavaScript
