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JavaScript - Extending The Date Constructor?
How to extend the constructor for the date object of the javasccript so that whenever a call is made to the constructor, I want to perform a particular action? Basically how to define wrappers for default javascript methods or objects like Date() so that I can perform some action and then invoke the original method?
So basically if I have something like var a = new Date(); I want it to (say) alert the value of the date everything Date() is called and then execute the default date constructor. TIA Similar Tutorialshi, i'm currently stumped by the following code. what's the point of using x.constructor.prototype? (highlighted in red) why not directly use x.prototype.classname to check whether 'classname' property is in this class? thx in advance Code: function getType(x) {
// If x is null, return "null"
if (x == null) return "null";
// Next try the typeof operator
var t = typeof x;
// If the result is not vague, return it
if (t != "object") return t;
// Otherwise, x is an object. Use the default toString( ) method to
// get the class value of the object.
var c = Object.prototype.toString.apply(x); // Returns "[object class]"
c = c.substring(8, c.length-1); // Strip off "[object" and "]"
// If the class is not a vague one, return it.
if (c != "Object") return c;
// If we get here, c is "Object". Check to see if
// the value x is really just a generic object.
if (x.constructor == Object) return c; // Okay the type really is "Object"
// For user-defined classes, look for a string-valued property named
// classname, that is inherited from the object's prototype
if ("classname" in x.constructor.prototype && // inherits classname
typeof x.constructor.prototype.classname == "string") // its a string
return x.constructor.prototype.classname;
// If we really can't figure it out, say so.
return "<unknown type>";
}
I had read from books that the constructor property of object is inherited from its prototype. And the prototype can be changed dynamically. New property can be added to or deleted from object even it was created before the prototype change. But I got confused on below codes. Code: function A()
{
this.title = "A";
}
function B()
{
this.title = "B";
}
document.write("<br>");
var b = new B();
document.write(b.constructor);
document.write("<br>");
document.write(B.prototype.constructor);
document.write("<br>");
B.prototype = new A();
document.write(b.constructor); // Suppose to output "function A() ..."
document.write("<br>");
document.write(B.prototype.constructor);
document.write("<br>");
B.prototype.constructor = B;
document.write(b.constructor);
document.write("<br>");
document.write(B.prototype.constructor);
document.write("<br>");
But the actual result (both IE and firefox) is Code: function B() { this.title = "B"; }
function B() { this.title = "B"; }
function B() { this.title = "B"; }
function A() { this.title = "A"; }
function B() { this.title = "B"; }
function B() { this.title = "B"; }
Please help me. thanks. Hi - In am learning Javascript and trying to understand why, the following line : Code: arguments.callee.superclass cannot be replaced by : Code: this.constructor.superclass In the following code sample : ( the explanation given is that if someone creates a subclass of PositionedRectangle, then this.constructor will refer to the new subclass constructor, not to PositionedRectangle - but why? 'this' here to my knowledge represents the object 'PositionRectangle' and if not I can't understand why not. ) Code: // Here is a simple Rectangle class.
// It has a width and height and can compute its own area
function Rectangle(w, h) {
this.width = w;
this.height = h;
}
Rectangle.prototype.area = function( ) { return this.width * this.height; }
// Here is how we might subclass it
function PositionedRectangle(x, y, w, h) {
// First, invoke the superclass constructor on the new object
// so that it can initialize the width and height.
// We use the call method so that we invoke the constructor as a
// method of the object to be initialized.
// This is called constructor chaining.
PositionRectangle.superclass = Rectangle;
arguments.callee.superclass .call(this, w, h);
// Now store the position of the upper-left corner of the rectangle
this.x = x;
this.y = y;
}
// Create a prototype for the subclass that inherits from the prototype
// of the superclass.
function heir(p) {
function f(){}
f.prototype = p;
return new f();
}
PositionRectangle.prototype = heir(Rectangle.prototype);
PositionRectangle.prototype.constructor = PositionRectangle;
I have a dice simulator. Basically, a user enters how many sides they want on their die, and then I digitally roll 2 of them. And produce the output in a document.writeln. I think I'm having trouble with the this.sides in the constructor function (in the head section). Also, I'm getting a syntax error in Safari : 25TypeError: 'null' is not an object (evaluating 'element.value') Am I not suppose to put the variable in the constructor function? Any help would be appreciated. <head> var element = document.getElementById("number"); var sides = element.value; function Die( ) { this.sides = sides; this.roll = function( ) { return parseInt((Math.random( ) * 1000) % this.sides) + 1; } } </script> </head> <body> <h1>Adam's Dice Rolling Game!</h1><br/> <form action="" method="post"> <p> <input type="text" name="number" id="number"/> </p> <p> <input type="button" value="Roll the dice!" id="roll_me"/> </p> </form> <script type="text/javascript"> var d = new Die( ); d.sides = sides; var rolled_value = d.roll( ); var r1 = document.getElementById( "roll_me" ); r1.onclick = function Die () { document.writeln ( d.roll () ); } </script> I need to detect the "name" of the constructor of an object. For example, myArray.constructor === Array is true, but I want something where that === 'Array' is true. I've heard of Object.constructor.name, but it's not widely compatible. Any ideas (preferably without involving regular expressions)? Thanks in advnce, Julian Hi All, Why is the Option constructor converting my text as follows? text = ' 1:30 pm' Option tag that gets generated: <option value="10">&nbsp;&nbsp;1:30 pm</option> How do I suppress the conversion of the & to & by the constructor? I've tried escaping the & but that's a no go. Thanks in advance for any help on this. JD I am trying to understand why I had an error, or why my solution worked. In my HTML I had: Code: <script language="JavaScript" type="text/javascript" src="Book.js"></script> <script language="JavaScript" type="text/javascript" src="Book_TEST.js"></script> Book.js said: Code: function Book(title, author)
{
this.title = title;
this.author = author;
}
Book.prototype.toString = function()
{ return '"' + this.title + '" by '+ this.author; };
var Book = new Book ("John", "Dough");
alert (Book); // displays "John Dough"
And, predictably, at this stage, the code worked. Book.js said: Code: var myBook = new Book ("JavaScript Tutorials", "Herong Yang");
However, at this point the JavaScript would crash and I'd get an error "Error: Book is not a constructor javascript." I drove myself nuts trying to figure out why the code wasn't working at this later point. Eventually, I copied another object: Code: /*
* Person class
*/
/**
* Person constructor
*
* @param {String} first
* The person's first name
* @param {String} last
* The person's last name
*/
function Person(first, last)
{
this.first = first;
this.last = last;
}
/**
* Create a string representation of this object
*
* @return {String} A string representation of this object
*/
Person.prototype.toString = function()
{
return this.first + " " + this.last;
};
/*
var person = new Person ("John", "Dough");
alert (person); // displays "John Dough"
*/
and then used find and replace to swap {Person, first, last} with {Book, title, author}, resulting in: Code: /*
* Book class
*/
/**
* Book constructor
*
* @param {String} title
* The Book's title
* @param {String} author
* The Book's author
*/
function Book(title, author)
{
this.title = title;
this.author = author;
}
/**
* Create a string representation of this object
*
* @return {String} A string representation of this object
*/
Book.prototype.toString = function()
{ return '"' + this.title + '" by '+ this.author; };
var Book = new Book ("John", "Dough");
alert (Book); // displays "John Dough"
Now, the code worked fine in both script. (i.e., no more error.) So far as I can tell, the only differences between the first and next version of Book.js are the comments and the whitespace. Am I missing something? Can the comments or whitespace somehow effect the logic with which this code has been executing? If I get an error like this again, is there an easier/better way to fix it than to essentially retype the code? Thanks in advance for helping me to understand this. Good day, I have the following code: Code: var img = new Image(); img.myProperty = 'something'; I've tried Image.prototype.myProperty and a few other things. It seems IE just doesn't want me extending the Image object. Is there a known work-around? Thanks I was wondering if there are any sites dedicated to ending javascript objects using the prototype property to give them features like trimming string, removing elements of arrays by name, removing duplicates in arrays, etc. Granted I have functions to do this but there's probably a ton of other good ones out there. Most things I've seen are frameworks like JQuery (which is awesome) but it doesn't extend these objects.
In the spirit of the season, I wanted to make it snow on my website. So I began digging. Eventually I ended up with a script that moved an image element down the page in a snowflake-like manner. The problem with it was it was dependant on an img element for every flake - simply no poor programming when using an Object Oriented programming language. So I decided I wanted to extend (in Java-speak; most of my programming background is in Java) the in-built Image object. The new object's src variable will lead to an image of the type of flake it is. (I want to be able to have more variance in images than a simple dot.) The new object will have a function that will allow it to move. A separate, unrelated function will control when each flakes move. I did some more research and read about prototyping on JavaScript Kit and here, but I still cant seem to get this to work. JS Lint says it's bug-free, but Firefox says "move()" is an invalid function. I am presuming the problem lies in my inability to fully grasp how to extend objects in JavaScript. Code: <html>
<head>
<script type="text/javascript">
Image.prototype.dFlake=dotFlake;
function dotFlake(xLocation,yLocation){
this.src = "simpleDotFlake.png";
this.x = xLocation;
this.y = yLocation;
}
dotFlake.prototype.move = fall;
function fall(){ // ^^ Belongs to dotFlake class.
this.style.position="absolute";
this.style.top = this.y;
this.style.left = this.x;
this.y= this.y + 1; // Falling is constant.
if (Math.random() > 0.5){ // Random direction, though.
this.x = this.x + 1;
} else{
this.x = this.x - 1;
}
}
function snow(flakes){ // Allows addition of different flakes later.
for (i in flakes){
i.move();
}
timer = setTimeout("snow()",1);
}
function startSnow(){
basicFlakes = new Array(new dotFlake(0,0));
snow(basicFlakes);
}
</script>
</head>
<body onload="startSnow()">
<h1>This is test text.</h1>
<img id="basicFlake" src="./simpleDotFlake.png" width="10" height="10" />
</body>
</html>
Any and all input is much appreciated. Thank you! ----------SOLUTION---------- ----------ORIGINAL PROBLEM---------- The second line of code. What does it do? It's confusing because it doesn't have a semicolon at the end and it doesn't end with (). Code: var centreicon = new GIcon(); centreicon.constructor centreicon.image = "http://maps.google.com/mapfiles/kml/pal3/icon31.png "; centreicon.shadow = "http://maps.google.com/mapfiles/kml/pal3/icon31s.png "; centreicon.iconSize = new GSize(12, 20); centreicon.shadowSize = new GSize(22, 20); centreicon.iconAnchor = new GPoint(6, 20); centreicon.infoWindowAnchor = new GPoint(5, 1); I found this on stackoverflow while trying to find a way to make my own icons on a map. With that being said. I'm still confused about how to apply the new graphic to a map. I don't see how they apply that picture to a coordinate. Does anyone know how to do that? Can I do this? Code: var centreicon = new GIcon(); centreicon.constructor centreicon.image = "http://maps.google.com/mapfiles/kml/pal3/icon31.png "; centreicon.shadow = "http://maps.google.com/mapfiles/kml/pal3/icon31s.png "; centreicon.iconSize = new GSize(12, 20); centreicon.shadowSize = new GSize(22, 20); centreicon.iconAnchor = new GPoint(6, 20); centreicon.infoWindowAnchor = new GPoint(5, 1); var marker = new GMarker( new GLatLng(-34.397, 150.644) , centreicon); map.addOverlay(marker); -------- A tad bit later -------- So this is the code I have on my testing site Even thought I'ved defined the the icon's image and location It does not show up on the map. What am I missing? Code: <!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="initial-scale=1.0, user-scalable=no" />
<style type="text/css">
html { height: 100% }
body { height: 100%; margin: 0; padding: 0 }
#map_canvas { height: 100% }
</style>
<script type="text/javascript"
src="http://maps.googleapis.com/maps/api/js?key=AIzaSyAWhjy3iZ8g6BZszj299c0yUY6ahKpSr1U&sensor=false">
</script>
<script type="text/javascript">
function initialize() {
var myOptions = {
center: new google.maps.LatLng(-34.397, 150.644),
zoom: 8,
mapTypeId: google.maps.MapTypeId.ROADMAP
};
var map = new google.maps.Map(document.getElementById("map_canvas"),myOptions);
var centreicon = new GIcon();
centreicon.constructor
centreicon.image = "http://maps.google.com/mapfiles/kml/pal3/icon31.png ";
centreicon.shadow = "http://maps.google.com/mapfiles/kml/pal3/icon31s.png ";
centreicon.iconSize = new GSize(12, 20);
centreicon.shadowSize = new GSize(22, 20);
centreicon.iconAnchor = new GPoint(6, 20);
centreicon.infoWindowAnchor = new GPoint(5, 1);
var marker = new GMarker( new GLatLng(-34.397, 150.644) , centreicon);
map.addOverlay(marker);
}
</script>
</head>
<body onload="initialize()">
<div id="map_canvas" style="width:100%; height:100%"></div>
</body>
</html>
Not sure if this is possible in javascript: I'm looking for two different dates (bill date and due date) on an invoice that are captured by OCR. If one of them exists, but the other does not, I want the empty field to be 14 days before (or after) the other. For example: if the bill date is 7/27/2010 and the due date was not captured, I want to set the due date as 8/10/2010 (14 days after the bill date). If the due date was captured as 8/10/2010, but the due date is blank, I want to assign the bill date as 7/27/2010 (14 days before the due date). if both dates have values, do nothing. Thanks. I have a drop down menu where people can select a month, day and year. Based on their selection, I want to show them an image. If their selection is >= July 26, 2010 but <= July 25, 2011, show the red image; If their selection is >= July 26, 2011 but <= July 25, 2012, show the white image; If their selection is >= July 26, 2012 but <= July 25, 2013, show the blue image; If their selection is >= July 26, 2013 but <= July 25, 2014, show the yellow image; I don't know how to compare a selected date to a range of dates like this. Hi, I've inherited a Form which calculates a future date based on a calculation and then inserts today's date and the future date into a database. The day part of the date is formatted as a number. This is fine, but up to 9 the numbers display in single figures with no leading zeros. I want them to display leading zeros (e.g. 01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11... 30, 31) So; 1/12/2010 is NOT wanted 01/12/2010 IS wanted The inherited code originally set the Month names as "Jan", "Feb" etc, and it was easy to kludge these to 01, 02... 12, but I suspect there's a more elgant solution to this as well, this bit of the code works so it's not as vital to neaten this but my database needs dd/mm/yyyy format (it's a third party email program). Code: </script>
<script type="text/javascript">
var todaysDate = new Date();
function updateExpiryDate(){
var weeklyMileage = document.getElementById('AvWeeklyMileage').value;
var expiryDate;
var weeks = 0;
var expiryDateString = '';
if (!isNaN(parseInt(weeklyMileage))){
weeks = 700/weeklyMileage;
expiryDate = new Date(todaysDate.getTime() + (1000 * 3600 * 24 * 7 * weeks));
var expiryDateString = expiryDate.getDate() + '/' + getMonthString(expiryDate.getMonth()+1) + '/' + expiryDate.getFullYear();
document.getElementById('expiryDate').innerHTML = expiryDateString;
document.getElementById('ShoeExpiryDate').value = expiryDateString;
} else {
document.getElementById('ShoeExpiryDate').value = '';
document.getElementById('expiryDate').innerHTML = 'Please enter a valid weekly average mileage'
}
}
function getMonthString(monthNumber){
var monthString = "";
switch(monthNumber){
case 1:
monthString = "01";
break;
case 2:
monthString = "02";
break;
case 3:
monthString = "03";
break;
case 4:
monthString = "04";
break;
case 5:
monthString = "05";
break;
case 6:
monthString = "06";
break;
case 7:
monthString = "07";
break;
case 8:
monthString = "08";
break;
case 9:
monthString = "09";
break;
case 10:
monthString = "10";
break;
case 11:
monthString = "11";
break;
case 12:
monthString = "12";
break;
default:
// do nothing;
}
return monthString;
}
function setTodaysDate(){
var todaysDateString = todaysDate.getDate() + '/' + getMonthString(todaysDate.getMonth()+1) + '/' + todaysDate.getFullYear();
document.getElementById('todaysDate').innerHTML =todaysDateString;
document.getElementById('DateOfPurchase').value = todaysDateString;
}
Can someone point me in the right direction please? Using Adobe Form Javascript validation, how would I do this code for Visual Basic in Javascript (non web) Code: If PurchaseDate.Value > Date Then
MsgBox ("PurchaseDate cannot be greater than Today's Date!")
Cancel = True
End If
Something along these lines but this isnt working: Code: If (PurchaseDate.Value > Date) Then
{
app.alert ("Purchase Date cannot be greater than Today's Date!");
}
Thanks Hello, I really need your help with one. How can I use the following code below to save the date from my popup window datepicker back into a var and relay it back onto its parent page? I can't seem to figure this out: Code: <html>
<head>
<script>
function open_cal() {
var str_html = ""
+ "<!DOCTYPE html>\n"
+ "<html lang=\"en\">\n"
+ "<head>\n"
+ "<meta charset=\"utf-8\">\n"
+ "<title>CALENDAR</title>\n"
+ "<link href=\"jq/jquery-ui.css\" rel=\"stylesheet\" type=\"text/css\">\n"
+ "<script src=\"jq/jquery.min.js\" type=\"text/javascript\"></" + "script>\n"
+ "<script src=\"jq/jquery-ui.min.js\" type=\"text/javascript\"></" + "script>\n"
+ "<script src=\"jq/datepicker.js\" type=\"text/javascript\"></" + "script>\n"
+ "</head>\n"
+ "<body>\n"
+ "<div id=\"text\" style=\"font: bold 10pt Tahoma\">Enter Approval Date:</div>\n"
+ "<div id=\"datepicker\"></div>\n"
+ "</body>\n"
+ "</html>"
var j = window.open("","CALENDAR","width=200,height=250,status=no,resizable=yes,top=200,left=200")
j.opener = self;
j.document.write(str_html);
}
</script>
</head>
<body>
<input onclick="open_cal()" type="button" value="Open" name="B1">
</body>
</html>
Datepicker.js: Code: $(function() {
$( "#datepicker" ).datepicker({
dateFormat: 'dd/mm/yy',
onSelect: function(dateText, inst) {
alert(dateText)
window.close()
}
})
});
Any help with this is greatly and mostly appreciated. Thanks in advance, Cheers, J Hi, I need to add days to a date in javascript, My requirement is as follows: Date is coming from a textbox. eg:- 26/07/2010 days from this statement var day1=document.getElementById('<%=HiddenDate.ClientID %>').value; an eg:- if the date is 28/01/2012 and days Needed to be added=5 the added date should be 02/02/2012. Can anybody help me? Thanks Jamuna hello there this is in vb script. but i dont where to post it. can any one hlep me out plzz I need to check if the date entered by user is within 5th date from current date. I am trying to do it this way entered date has month and date value Code: sResvDate = 01/24 Set sMaxDays to getdate(5) but get date will give year too. and how do i compare if it less than 5th day or not. Hi folks, i am trying to generate a dynamic datefield with date mask "mm/dd/yyyy" and trying to insert it into Oracle db ...i still got the error ORA invalid month ehich means the date filed is not recognized as date: below is what i am doing : newStartDate = document.createElement( 'INPUT' ); newStartDate.setAttribute('type','Date'); newStartDate.setAttribute('id1','id'+ elementid+elementrow); newStartDate.setAttribute('name','StartDateName'+ elementid+elementrow); newStartDate.size=8; newStartDate.style.backgroundColor= bgc; any help thanks ?? Also i want to add a datepicke to this textbox..how it is posible / other option is to use Jquery datepicker but could not know how to impement it thanks again |
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