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JavaScript - Alternative To Object.constructor.name
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 Similar TutorialsI 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. hi, 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> 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 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 Hi, every time I try and alert: [ { number:0, secondnumber:0 }, { number:2, secondnumber:1 }, { number:1, secondnumber:2 } ] it just shows [object object], [object object], [object object]. Why is this and what can I do to make the record be shown as it is above in an alert? Thanks. I can't get any info from Firebug except that one line, uncaught exception [object Object]. The code fully worked, then I needed to make it dynamically create Sortables from the scriptaculous library based on how many X were in a table in my database, which I've done, and I'm thinking it may be a simple slight parse error of some type, I'm not too good with Javascript, because now my script barely works. I've double checked the script's source code, the PHP variables are exactly what they should be. Code: print<<<HERE
Sortable.create('sortlist$box', { tag: 'img', overlap:'horizontal',constraint:false, containment: $list, dropOnEmpty: true,
onChange: function(item) {
var list = Sortable.options(item).element;
if(changeEffect) changeEffect.cancel();
changeEffect = new Effect.Highlight('changeNotification', {restoreColor:"transparent" });
},
onDrop: function(item) {
var thing=Sortable.options(item).element.identify();
var anchors = document.getElementById(thing).childNodes.length-2;
if(anchors > 20){
alert('This box had 20 creatures in it already, your last action has not been saved.');
window.location.reload();
}
else{
new Ajax.Request("saveImageOrder.php", {
method: "post",
parameters: { data: Sortable.serialize("sortlist$box") }
});
}
}
});
HERE;
$box++;
}
?>
});
</script>
if you solve this I'll send ya $10 via paypal I created a method for displaying an object's properties: Code: renderfunction = false;
function showProperty (object, property)
{
document.write ('<td class="type">' + (typeof object[property]) + '</td>'
+ '<td class="name">' + property + '</td>');
document.writeln('<td class="value">' +
(
(typeof object[property] != 'function')
? object[property]
:(
(property != 'showProperties')
? (
renderfunction
? object[property]()
: ('<span class="self">NOT RENDERED</span>')
)
: ('<span class="self">THIS</span>')
)
)
+ '</td>');
document.writeln('<td class="hasOwnProperty" >'
+ (
object.hasOwnProperty(property)
? "Local"
: "Inherited"
)
+ '</td>');
if (typeof object[property] == 'function')
{
document.writeln ('<td class="function">' + object[property] + '</td>');
}
else
{
document.writeln ('<td class="function"> </td>');
}
}
As long as renderfunction = false, the object is fine coming out of this function. However, if I change renderfunction to true, all my properties become undefined. Why isn't this working as I expect it to? How should I fix it? Thanks in advance, -Brian. Hi all, I'm stumped on finding a way in javascript to create an object factory whose instances are also object factories. In short I want something like that below, but no joy ... any clues? Code: function createClass () {
return new createClass()
function createClass() {
return new createInstance ()
function createInstance () {
//Default properties, values and methods which might later be extended
}
}
}
var createDoor = createClass();
var door1 = createDoor();
var door2 = createDoor();
var createChair = createClass();
var chair1 = createChair ();
var chair2 = createChair ();
I'm writing a program that involves a network of interconnected nodes (or simply objects in my example below). It depends on being able to access properties of an object's linked objects (a bit oddly worded, sorry)... Problem is I'm not sure how to properly access those properties... see below please. <script> //This is an example of a problem im having in my own code... //I want to access the name of the object within the links array wintin the object... var objA = {name: "Object A", links: [objB, objC]}; var objB = {name: "Object B", links: [objC, objD, objE]}; var objC = {name: "Object C", links: [objB]}; var objD = {name: "Object D", links: [objE]}; var objE = {name: "Object E", links: [objD]}; //ex: I want to access the name of Object A's first link... console.log(objA.links[0].name); </script> I'm hoping to get "Object B"... But instead I get: TypeError: Result of expression 'objA.links[0]' [undefined] is not an object. Is there another way around this? Any thoughts are appreciated. Ignore post (if mod, please delete)
Hello together! I generate html code with jsp. In that jsp there a several framesets and frames. And yes i know, frames are not really up to date but it's an old program and i have to deal with it now. Anyway, in the top frameset i have an onload attribute like onload="load()". In the function load i want to access the Element.prototype object. But unfortunately typeof Element gives me "undefined". So i looked a little deeper and found that window.toString() gives me "[object]" and not as expected "[object window]" so somehow my window doesn't know that its construcor is Window. window.construcor is "undefined" as well. And i don't have access to the Element object. I really don't know where the error could be. When the page is loaded and i access the same window over the console, then everything is right. But in my function a can't get access to the objects i need. I also don't know what part of the code could be useful to post here, but maybe someone had a similar problem before? i should say that this problem only occurs in IE8. In IE9 it works perfectly. Has anyone any idea?? ----------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>
Quote: menu: function( a, b ) { $( b ).observe( 'click', function( event ) { event.stop(); if( $( a ).visible() ) { $( a ).hide(); $( b ).removeClassName( 'selected' ); document.stopObserving( 'click' ); } else { $( a ).show(); $( b ).addClassName( 'selected' ); document.observe( 'click', function( e ) { if( e.target.id != a && e.target.id != b && !Element.descendantOf( e.target, $( a ) ) ) { $( a ).hide(); $( b ).removeClassName( 'selected' ); document.stopObserving( 'click' ); } }); } }); $$( '#' + b + ' > a' ).each( function( element ) { element.observe( 'click', function( event ) { $( a ).hide(); $( b ).removeClassName( 'selected' ); document.stopObserving( 'click' ); }); }); } This work's perfrect accept when i use it with others on the menu it leaves the other ones open, how do i get it to close the open one when i open a new menu.. Thanks. Hello. Is there any way to get the variable name of an object from inside the object? E.g. PHP Code: function Bla(){ this.write = function(){ document.write(<objectname>); } } obj1 = new Bla(); obj1.write(); //Outputs obj1 Here is my script: PHP Code: function myTimer(seconds, obj){ this.seconds = seconds; this.obj = obj; this.startTimer = function(){ if(this.seconds>0){ this.seconds--; this.obj.innerHTML = this.seconds; this.timer = setTimeout("Timer.start()",1000); } } } Timer = new Timer(10, obj); Timer.startTimer(); Now the problem is that the variable that contains the object must be named "Timer". This way I cannot create new timer objects with different variable names I have tried: this.timer = setTimeout("this.start()",1000); but it doesn't work. That's why it would be good to detect the variable name and instead use something like this: this.timer = setTimeout(varname+".start()",1000); I would rather not have to pass the variable name through a parameter like this: Timer1 = new Timer(10, obj, "Timer1"); Thanks in advance. is there any alternative to document.write() which writes only in a specific part of document, does not overwrite whole document. and yeah, in this case the document.getElementById().innerHTML dosent work either, coz its in a loop, here's the code if you wanna see: Code: if (aa==1)
{
for (i=0;i<a.length;i++)
{
c = txt;
b = a[i].childNodes[0].nodeValue; // a is already assigned someplace in a xml document.
txt = (b==" T4 ")? "T4 <br />": "";
document.write(c);
}
}
Note: in the above code, the code: Code: txt = (b==" T4 ")? "T4 <br />": ""; is same as (also can be written as ) the code : Code: if (b==" T4 ")
{
txt = "T4 <br />" ;
}
else
{
txt = "" ;
}
Issue: I have a java script that bring up a simple password box, It works great in Chrome, Safari, firefox but I get a box in Internet explorer asking my customers to take another step to allow access. This is not good, Customers did not now what to do. Error: This website is using a scripted window to ask you for information. If you trust this website, click here to allow scripted windows Microsoft response: "Internet Explorer has blocked a website from using a small program (called a script) to display a separate window. Hackers sometimes use scripted windows to mimic legitimate windows, such as login screens, that appear on websites. If you trust the website and want to allow the scripted window, click the Information Bar, and then click Temporarily Allow Scripted Windows. To always allow scripted windows, check the Allow websites to prompt for information using scripted windows custom security setting." Objective: I now there is likely no way to by pass this, so i need a different solution. Possible a Form Box to be present on the site that when information is entered it passes the password to the javascript code to allow access? Please help, this is actually urgent as I have already lost a customer :-( Code: : <script>
function getStyle()
{
var temp = document.getElementById("admintable").style.visibility;
return temp;
}
function switchMain()
{
var isAuthed = authenticate();
if(isAuthed){
var current = getStyle();
if( current == "visible" ){
document.getElementById("admintable").style.visibility = "hidden";
}else{
document.getElementById("admintable").style.visibility = "visible";
}
}
}
function authenticate()
{
if(readCookie('authenticated')!=null)
{
return true;
}
else{
var password=prompt("Enter Code","")
if (password =="1234")
{
createCookie('authenticated',true);
return true;
}
}
return false;
}
function readCookie(name) {
var nameEQ = name + "=";
var ca = document.cookie.split(';');
for(var i=0;i < ca.length;i++) {
var c = ca[i];
while (c.charAt(0)==' ') c = c.substring(1,c.length);
if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
}
return null;
}
function createCookie(name,value,days) {
if (days) {
var date = new Date();
date.setTime(date.getTime()+(days*24*60*60*1000));
var expires = "; expires="+date.toGMTString();
}
else var expires = "";
document.cookie = name+"="+value+expires+"; path=/";
}
</script>
Here is what I found online: http://www.anyexample.com/webdev/jav...lternative.xml UPDATE: I am a n00b, I need to incorporate this code below to the one above. Thanx Philip Code: <input type = "password" name = "pwd" id = "pwd" onchange = checkPassword(this.value)"
<script type = "text/javascript">
function checkPassword(which) {
if (which != "1234") { // password is visible!!!
alert ("Incorrect password - please try again");
document.getElementById("pwd").value ="";
return false;
}
else {
alert ("Password is correct!");
//do more stuff here, e.g create the cookie
}
}
</script>
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