A module mode of Javascript_javascript skills
Douglas Crockford has taught a useful singleton pattern that implements this rule, and I think his pattern will be beneficial for your YUI-based applications. Douglas calls it the module pattern. It works as follows:
1. Create a namespace object: If you use YUI, you can use the YAHOO.namespace() method: YAHOO.namespace("myProject"); This allocates an empty myProject object, which is A member of YAHOO (will not be overwritten if myProject already exists). Now we can start adding members of YAHOO.myProject.
2. Assign an anonymous function return value to your namespace object:
YAHOO.myProject.myModule = function () {
return {
myPublicProperty: "I am accessed as YAHOO.myProject.myModule.myPublicProperty.";
myPublicMethod: function () {
YAHOO.log("I was accessed as YAHOO.myProject.myModule.myPublicMethod.");
}
};
}(); // This bracket causes the anonymous function to be executed and returned
Note the last line with the closing brace followed by the parenthesis () - this notation causes the anonymous function to be executed immediately, returning an object containing myPublicProperty and myPublicMethod. As soon as this anonymous function returns, the returned object is accessed as YAHOO.myProject.myModule.
3. In the anonymous function, add "private" methods and variables before the return statement. So far, we've just assigned myPublicProperty and myPublicMethod directly into YAHOO.myProject.myModule. Additionally, this pattern supports increased utility when we place some code before the return statement.
YAHOO.myProject.myModule = function () {
//"Private" variable:
var myPrivateVar = "I can only be accessed within YAHOO.myProject.myModule.";
//Private method:
var myPrivateMethod = function () {
YAHOO.log("I can only be accessed within YAHOO.myProject.myModule.");
}
return {
myPublicProperty: "I can access it as YAHOO.myProject.myModule.myPublicProperty Accessed. "
myPublicMethod: function () {
YAHOO.log("I can be accessed as YAHOO.myProject.myModule.myPublicMethod.");
//In myProject, I can access private Variables and methods
YAHOO.log(myPrivateVar);
YAHOO.log(myPrivateMethod());
//The native scope of myPublicMethod is myProject, and we can use "this" to access public members.
YAHOO.log(this.myPublicProperty);
}
};
}();
In the above code, we return from an anonymous function An object with two members. Inside YAHOO.myProject.myModule, it can be accessed using this.myPublicProperty and this.myPublicMethod respectively. Outside YAHOO.myProject.myModule, public members can be accessed using YAHOO.myProject.myModule.myPublicProperty and YAHOO.myProject.myModule.myPublicMethod.
Private variables myPrivateProperty and myPrivateMethod can only be accessed by the anonymous function itself or by members of the returned object. Although anonymous functions execute and terminate immediately, they are still retained by the power of closure - the rule that variables local to a function are retained after the function returns. Our two private variables will not be destroyed as long as YAHOO.myProject.myModule requires them.
4. Practice this model. Let's look at a common application case of this pattern. Suppose you have a list, and some items on the list can be dragged. There is a dragging CSS class on the item to which dragging is applied.
- One item
- Two items
- Three items
<script> <br>YAHOO.namespace("myProject"); <br>YAHOO.myProject.myModule = function () { <br>// Private shorthand reference for YUI utilities: <br>var yue = YAHOO.util.Event, <br>yud = YAHOO.util.Dom; <br>//Private method <br>var getListItems = function () { <br>// Note that other private variables are used here, including the abbreviation of "yud" YAHOO.util.Dom: <br>var elList = yud.get("myList"); <br>var aListItems = yud.getElementsByClassName( <br>"draggable", //Get only items with CSS class "draggable"<br>"li", //Return only list items<br>elList //Limit the search to the child of the changed element<br>); <br>return aListItems; <br>}; <br>//This returned object will become YAHOO.myProject.myModule: <br>return { <br>aDragObjects: [], //Externally accessible, storage DD Object <br>init: function () { <br>//Until the DOM is fully loaded, the list items will not be draggable: <br>yue.onDOMReady(this.makeLIsDraggable, this, true); <br>}, <br>makeLIsDraggable: function () { <br>var aListItems = getListItems(); //Those elements we can drag<br>for (var i=0, j=aListItems.length; i<j; i ) { <br>this.aDragObjects.push(new YAHOO.util.DD(aListItems[i])); <br>} <br>} <br>}; <br>}(); <br>//Above The code has been executed, so we have immediate access to the init method: <br>YAHOO.myProject.myModule.init(); <br></script>
This is a simple example, It's intentionally detailed - if we did it this way we would undoubtedly be able to make it more compact. This pattern scales well as the project becomes more complex and its API increases. In this way, it avoids the global namespace, provides externally accessible API methods, and supports protected or "private" data and methods.
- [1]Original text: 《a javascript module pattern》. This is on the YUI blog. It may not be open in some places. You can search for English reprints or use the search engine cache to view it.
- [2]"A JavaScript Module Pattern – A module pattern for JavaScript" This is someone else’s translation. I have referenced it a lot, but it seems inconvenient to read. This is my translation. One reason for this article, and of course the main reason is that this article is the most basic article for learning YUI. The entire YUI module model is based on this.
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