OOP & JavaScript

In previous article I have presented you a small example of code, which allows you to use the three pillars of OOP theory in JavaScript. The way it is accomplished is a little tricky, but I have afforded mysefl to modify extend function a bit, to give a possibility of having a static constants for classes (in fact, the constants in result are just conventional, of course). Here I will provide a special example for it.

So, the basic functions (I’ll say it again, I have taken them from AJAXPath and AJAXPatterns sources):


function Class() { };

Class.prototype.construct = function() { };

Class.extend = function(def) {

    var classDef = function() {
        if (arguments[0] !== Class) {
            this.construct.apply(this, arguments);
        }
    };

    var proto = new this(Class);
    var superClass = this.prototype;

    for (var n in def) {
        var item = def[n];
        if (item instanceof Function) item.$ = superClass;
                else classDef[n] = item;
        proto[n] = item;
    }

    classDef.prototype = proto;
    classDef.extend = this.extend;

    return classDef;
};

Through the usage of these three functions, you have a possibility to build a relatively serious and deep-constructed frameworks, not loosing the code readability and a way to find a needed place to change fast. Plus OOP possibilities, of course

These three functions were used as a foundation of OOP-Drag’n’Drop framework for a major project in Java+Wicket. I will provide later this code itself, if it will be possible and allowed by a company.

Let’s return to business. For a code like this you need an example. I have build a little script that emulates a Windows OS, I hope it will match your needs:


/* some helping functions */

function getInstanceOf(className) {
    // creates an object using the class name
    return eval('new ' + className + '()');
}

function pause(millis) // pauses the execution of script
    // for a specified number of milliseconds
{
    var time = new Date();
    var curTime = null;
    do { curTime = new Date(); }
        while( curTime - time < millis);
}

/* === Abstract Operating System === */

var AbstractOS = Class.extend({

    construct: // constructor, parameter is a computer type
        function(computerClassName) {
            // coumputer that runs OS
            this._computer = getInstanceOf(computerClassName);
        },

    getComputer: function() { return this._computer; },

    reboot: // OS reboot
        function() {
            return this.getComputer().shutDown() &&
                   this.getComputer().startUp();
        },

    shutDown: // OS shuts down
        function() { return this.getComputer().shutDown(); },

    startUp: // OS starts
        function() { return this.getComputer().startUp(); },

    exec: // an abstract (conventionally) method to execute commands
        function(commandStr) { return false; },

    cycle: // starting OS, executing command, shutting OS down
        function(cmdStr) {
            return this.startUp() && this.exec(cmdStr) &&
                                     this.shutDown();
        }

});

/* === Blue Screen of Death === */

var BSOD = Class.extend({

    launch: // launch
        function() {
            alert('You see the BSOD');
            return true;
        }

});

/* === MS Windows Operating System === */

var MSWindows = AbstractOS.extend({
    // inherits abstract OS

    // messages are static constants (conventional)
    STARTUP_MSG: 'Windows Starting',
    EXEC_MSG: 'This program has performed an illegal operation',
    REBOOT_MSG: 'Do you really want to reboot your computer?',

    construct: // constructor, parameter is a type of computer
        function(computerClassName) {
            // calling parent constructor
            arguments.callee.$.construct.call(this, computerClassName);
            // a cached instance of death screen (it will be the only one)
            this._bsod = new BSOD();
        },

    getBSOD: function() { return this._bsod; },

    reboot: // reboot is overriden
        function() {
            // displaying message
            alert(MSWindows.REBOOT_MSG);
            // calling parent method
            return arguments.callee.$.reboot.call(this);
        },

    shutDown: // shutting off is overriden
        function() {
            // calling BSOD and if it was successfull,
            // call a parent method, boolean result is returned
            return (this.getBSOD().launch() &&
                    arguments.callee.$.shutDown.call(this));
        },

    startUp: // booting is overriden
        function() {
            // if parent method was succesfully executed
            if (arguments.callee.$.startUp.call(this)) {
                // do some required operations
                pause(400);
                //setTimeout("alert('Windows Starting')", 400);
                // say we succesfully started
                alert(MSWindows.STARTUP_MSG);
                return true;
            } else return false; // no is no
        },

    exec: // command execution is overriden
        function(commandStr) {
            // if command is valid - say a result
            // else just shut down
            return commandStr
                ? alert(MSWindows.EXEC_MSG)
                : this.shutDown();
        }

});

/* === Usual Computer === */

var SimpleComputer = Class.extend({

    startUp: // alert when starts
        function() { alert('Starting Up'); return true; },

    shutDown: // alerts when shutting down
        function() { alert('Shutting Down'); return true; }

});

/* test function */

function perform() {
    // OS is initialized on computer (installation)
    var testOs = new MSWindows('SimpleComputer');
    // starting OS
    testOs.startUp();
    // executing a trivial command
    testOs.exec('ls -laF');
    // shutting OS off
    testOs.shutDown();
}

NB! (pay attention not to put a comma after the last method definition in class, or IE will fail)

If you have disliked the previous example – I can offer you a useful class, that really helps if the idea of DOM element intersects with the manipulated object idea inside your project:


var ElementWrapper = Class.extend({

    construct:
        function(elementId) {
            this.elementId = elementId;
            this.element = null;
            this._initializeElement();
        },

    _initializeElement:
        function() {
            var docElm = document.getElementById(this.elementId);
            if (!docElm) {
                this.element = document.createElement('div');
                this.element.id = this.elementId;
            } else {
                this.element = docElm;
            }
            this._assignListeners();
        },

    _assignListeners:
        function() {
            . . .
        },

    . . .

    reassignTo:
        function(elementId) {
            this.elementId = elementId;
            this.element = null;
            this._initializeElement();
        }

});

You can comfortly extend this class with other classes expanding the DOM elements functionality. Also, you can use a code like this:


var someElement = new ElementWrapper('someElmId');

…and someElement object will be linked to element (wrapping an element) with id SomeElmId. To access it – as a DOM element – you can ask someElement.element property.

The following class inherits ElementWrapper and allows to work with element as a fully-functional graphic object (using some functions from previous article: getElmAttr, setElmAttr, findOffsetHeight, getPosition, getAlignedPosition)

As it is for some functions from previous article, the code is changed through times – in this case it was parallelly simplified and growed in functionality:


var DND_NS     = 'dnd'; // to use in getAttributeNS and setAttributeNS

var DND_LWIDTH_ATTR  = 'localWidth';
var DND_LHEIGHT_ATTR  = 'localHeight';
var DND_LTOP_ATTR   = 'localTop';
var DND_LLEFT_ATTR   = 'localLeft';
var DND_BTOP_ATTR   = 'baseTop';
var DND_BLEFT_ATTR   = 'baseLeft';

var GraphicalElementWrapper = ExpandedElementWrapper.extend({

 _assignListeners:
  function() {
   // do not assign events listeners if they are not required
  },

    // ========[ functions to work with required attributes ]==========

    /* localLeft, localTop -- coordinates of the lop left element corner,
                              taking the [scrolling] offset into account;
       localWidth, localHeight -- the real height and width of element
       baseLeft, baseTop -- coorfinates of top left element corner
                            without the [scrolling] offset */

 setLocalWidth:
  function(localWidth) {
   setElmAttr(this.element, DND_LWIDTH_ATTR, localWidth + 'px', DND_NS);
  },

 setLocalHeight:
  function(localHeight) {
   setElmAttr(this.element, DND_LHEIGHT_ATTR, localHeight + 'px', DND_NS);
  },

 setLocalLeft:
  function(localLeft) {
   setElmAttr(this.element, DND_LLEFT_ATTR, localLeft + 'px', DND_NS);
  },

 setLocalTop:
  function(localTop) {
   setElmAttr(this.element, DND_LTOP_ATTR, localTop + 'px', DND_NS);
  },

 setBaseLeft:
  function(baseLeft) {
   setElmAttr(this.element, DND_BLEFT_ATTR, baseLeft + 'px', DND_NS);
  },

 setBaseTop:
  function(baseTop) {
   setElmAttr(this.element, DND_BTOP_ATTR, baseTop + 'px', DND_NS);
  },

 getLocalWidth:
  function() {
   return getElmAttr(this.element, DND_LWIDTH_ATTR, DND_NS);
  },

 getLocalHeight:
  function() {
   return getElmAttr(this.element, DND_LHEIGHT_ATTR, DND_NS);
  },

 getLocalLeft:
  function() {
   return getElmAttr(this.element, DND_LLEFT_ATTR, DND_NS);
  },

 getLocalTop:
  function() {
   return getElmAttr(this.element, DND_LTOP_ATTR, DND_NS);
  },

 getBaseLeft:
  function() {
   return getElmAttr(this.element, DND_BLEFT_ATTR, DND_NS);
  },

 getBaseTop:
  function() {
   return getElmAttr(this.element, DND_BTOP_ATTR, DND_NS);
  },

 getOffsetWidth:
  function() {
   return this.element.offsetWidth;
  },

 getOffsetHeight:
  function() {
   return this.element.offsetHeight || this.element.style.pixelHeight || findOffsetHeight(this.element);
  },

    // =======[ / function to set required attributes ]=========

 show: // show element
  function() {
   this.element.style.display    = '';
   this.element.style.visibility = 'visible';
  },

 hide: // hide element
  function() {
   if (this.element.style.display != 'none') {
    this.element.style.display  = 'none';
   }
  },

 blank: // make element "blank"
  function() {
   if (this.element.style.display != '') {
    this.element.style.display    = '';
    this.element.style.visibility = 'hidden';
   }
  },

 makeBlock: // return the element from blank or hidden state
  function() {
   if (this.element.style.display != 'block') {
    this.element.style.display  = 'block';
   }
  },

 isPointInside: // is point inside the element, point in {x, y} format
  function(curPoint) {
   var localRight  = parseInt(this.getLocalLeft()) + parseInt(this.getLocalWidth())
                                       + this.element.scrollLeft;
      var localBottom = parseInt(this.getLocalTop())  + parseInt(this.getLocalHeight())
                                       + this.element.scrollTop;
      return (parseInt(this.getLocalLeft()) < curPoint.x) &&
          (parseInt(this.getLocalTop())  < curPoint.y) &&
          (localRight > curPoint.x) && (localBottom > curPoint.y);
     },

 isElementNear: /* is element is positioned near the passed element
            (overlaps the region of this element with more than a half of the current element region) */
     function(graphicalElement) {
      if (graphicalElement) {
    var elmCurPos = findPos(graphicalElement.element);
    var elmHalfHeight = parseInt(graphicalElement.getLocalHeight())/2;
    var elmHalfWidth = parseInt(graphicalElement.getLocalWidth())/2;
    var localLeft = (parseInt(this.getLocalLeft()) > 0 ? parseInt(this.getLocalLeft()) : 0);
    var localTop = (parseInt(this.getLocalTop()) > 0 ? parseInt(this.getLocalTop()) : 0);
    var leftCorrect = (elmCurPos.x > (localLeft - elmHalfWidth)) &&
          (elmCurPos.x < (localLeft + parseInt(this.getLocalWidth()) - elmHalfWidth));
    var topCorrect = (elmCurPos.y > (localTop - elmHalfHeight)) &&
            (elmCurPos.y < (localTop + parseInt(this.getLocalHeight()) - elmHalfHeight));
    return leftCorrect && topCorrect;
   } else return false;
  },

 isElementInside: // is passed element is inside current element
  function(graphicalElement) {
   if (graphicalElement) {
    var elmCurPos = findPos(graphicalElement.element);
    var elmHalfHeight = parseInt(graphicalElement.getOffsetHeight())/2;
    var elmHalfWidth = parseInt(graphicalElement.getOffsetWidth())/2;
    return this.isPointInside({x:(elmCurPos.x + elmHalfWidth),
            y:(elmCurPos.y + elmHalfHeight)})
   } else return false;
  },

 isLeftSide: // is the point ({x, y}) on the left side of elements region
  function(curPoint) {
   var elmHalfWidth = parseInt(this.getLocalWidth())/2;
   var localLeft = (parseInt(this.getLocalLeft()) > 0 ? parseInt(this.getLocalLeft()) : 0);
   return (curPoint.x >= localLeft) && (curPoint.x < (localLeft + elmHalfWidth));
  },

 isRightSide: // is the point ({x, y}) on the right side of elements region
  function(curPoint) {
   var elmHalfWidth = parseInt(this.getLocalWidth())/2;
   var localRight = ((parseInt(this.getLocalLeft()) > 0
                    ? parseInt(this.getLocalLeft())
                    : 0)) + parseInt(this.getLocalWidth());
      return (curPoint.x <= localRight) && (curPoint.x > (localRight - elmHalfWidth));
     },

 inTopOf: // is the point ({x, y}) on the top side of elements region
  function(curPoint) {
   var localTop  = (parseInt(this.getLocalTop()) > 0 ? parseInt(this.getLocalTop()) : 0);
   var localHeight = (parseInt(this.getLocalHeight()) > 0 ? parseInt(this.getLocalHeight()) : 0);
   if (this.element.clientHeight && (this.element.clientHeight < localHeight))
                localHeight = this.element.clientHeight;
      return ((curPoint.y > localTop) && (curPoint.y <= (localTop + (localHeight / 10))));
     },

 inBottomOf: // is the point ({x, y}) on the bottom side of elements region
  function(curPoint) {
   var localTop  = (parseInt(this.getLocalTop()) > 0 ? parseInt(this.getLocalTop()) : 0);
   var localHeight = (parseInt(this.getLocalHeight()) > 0 ? parseInt(this.getLocalHeight()) : 0);
   if (this.element.clientHeight && (this.element.clientHeight < localHeight))
                localHeight = this.element.clientHeight;
      return ((curPoint.y >= (localTop + localHeight - (localHeight / 10))) &&
                    (curPoint.y < (localTop + localHeight)));
     },

 recalc: // recalculates the element's coordinates
        /* baseOffset in the very most cases is
           { x: this.element.scrollLeft, y: this.element.scrollTop } */
     function(baseOffset) {

      var pos = findPos(this.element);

      this.setBaseLeft(pos.x);
      this.setBaseTop(pos.y);
      this.setLocalLeft(pos.x - (baseOffset ? baseOffset.x : 0));
      this.setLocalTop(pos.y - (baseOffset ? baseOffset.y : 0));
      this.setLocalWidth(parseInt(this.getOffsetWidth()));
      this.setLocalHeight(parseInt(this.getOffsetHeight()));
     },

 addOffset: // adds the offset to element, offset is in {x, y} format
  function(offsetXY) {
   this.setLocalLeft(parseInt(this.getBaseLeft()) - offsetXY.x);
   this.setLocalTop(parseInt(this.getBaseTop()) - offsetXY.y);
  },

    copyElmRectParameters: // copy attributes of this element to another
     function(fromElm, toElm) {
      toElm = toElm || this.element;
      setElmAttr(toElm, DND_BTOP_ATTR, getElmAttr(fromElm, DND_BTOP_ATTR, DND_NS), DND_NS);
      setElmAttr(toElm, DND_BLEFT_ATTR, getElmAttr(fromElm, DND_BLEFT_ATTR, DND_NS), DND_NS);
      setElmAttr(toElm, DND_LTOP_ATTR, getElmAttr(fromElm, DND_LTOP_ATTR, DND_NS), DND_NS);
      setElmAttr(toElm, DND_LLEFT_ATTR, getElmAttr(fromElm, DND_LLEFT_ATTR, DND_NS), DND_NS);
      setElmAttr(toElm, DND_LWIDTH_ATTR, getElmAttr(fromElm, DND_LWIDTH_ATTR, DND_NS), DND_NS);
      setElmAttr(toElm, DND_LHEIGHT_ATTR, getElmAttr(fromElm, DND_LHEIGHT_ATTR, DND_NS), DND_NS);
     }

});

Both of these classes, I hope, will help you with making DOM elements more graphical-base (for example, for Drag’n’Drop (here I’ve extended the dragging nodes classes, regions classes, receiving regions classes and drag helper – from GraphicElementWrapper, and the main container – from ElementWrapper) or, for example, for the web-application which emulates the windows-based application (here I have extended the draggable elements from GraphicElementWrapper, but menu, status bar and the worktable – from ElementWrapper).

Seems that’s all for now. Good luck in JS-contruction-deeds :).

about this…

🗓️ Timeline
  • 16 Practical Solutions for Javascript

    That’s all, seems, for now. The article is ready for corrections (if they will appear :) ), I can pass to the next ones :). In the next-article I want to tell about OOP in JavaScript and make a few simple but useful examples of classes. I hope this article saved some of your man-hours that you may potentially had spent in the fighting with variable browsers quirks.

    The complete examples of usage are too huge for this article, so I’ll pass them to the next article, and now we’ll proceed further. You may notice two simple examples in the points _2_, _5_ and _15_.

#javascript