Extending An Object Whose Constructor Takes Arguments?
Jan 2, 2011
I'm sure this question has been asked many times before, but I can't seem to get the correct terms to find the answer in Google.I understand basic JavaScript inheritance. However, everything I've read makes the inheritance work something like this:
Code JavaScript:
var ChildClass = new Function();
ChildClass.prototype = new ParentClass();
ChildClass.constructor = ChildClass;
That's fine, but what happens when ParentClass's constructor needs parameters?As an example, look at the following code:
Code JavaScript:
function Furniture(color){
this.color = color;[code)....
How could I "copy" Furniture's constructor into the Chair object? Better yet, how could I copy Furniture's constructor and then add some functionality to it?
Sorry, bad title. Anyway, is there a way to pass the arguments to an object instantiated via a constructor using the arguments object and have it expanded, so to speak, so that it doesn't appear as a single argument? I'm sorry, this explanation is just atrocious, but I can't think of exactly how to word it. Maybe an example...
Take for instance Function.apply. It takes 1-2 arguments, the first being the object to use as the context, and the second being either an array or an instance of the arguments object which are to be the arguments for the function. I want to do something similar but I want to also basically use the new operator so that I get back an object.
Here's a snippet of some of my code, maybe this will help:
I encountered some code in "Javascript the good part" from Douglas Crockford.There is a way to passing callback function as second argument to string.replace() method.
Code:
var entity = { quot: '"', lt: '<',
[code]....
1. How do I know what the number of parameters should be in callback function ( function(a,b) ) ?
2. How do I know what will be passed in as a and b when I am defining the callback function?
Code: function BaseController(el) { var that = this; this.defaultAction = function() {
[Code]....
What is the proper method here so that el will be defined in the super "class".? I know I saw something on stack overflow a couple of days ago but can not seem to find it again.
admin: Something is up with the code tags, why the system is double posting the code. Does HIGHLIGHT=JS not exists anymore? – That seemed not be working.
How would I go about copying all the prototype functions AND the constructor from one object into another object, and then call them?
I know I can use this.example.call(this), but that's not an acceptable solution. I want to deploy this style over dozens, potentially hundreds of 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 (http://mckoss.com/jscript/object.htm), 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.
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. (preferably without involving regular expressions)?
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?
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.
I have a requirement to override the constructor of a javascript class. I have to execute the current constructor code and then call a javascript method. Basically, I need to execute a javascript method whenever an object of that particular class is created in addition to whatever is being done now. I do not want to copy and paste the current constructor code and override the initcomponent method. I am looking for an alternative for that.
I need to create a constructor for a computer object. This object must have three properties: speed, and mem_live mem_dead. Then I need to create a new object using this constructor and then have its properties displayed on the screen.Look at what I'm up to so far:
function Computer(speed, mem_live, mem_dead) { this.speed = speed;
function show() { var s = '' ; for (var i = 0; i<arguments.length; s += ' '+arguments[i++]) ; typeof(window) != 'undefined' ? window.alert(s) : WScript.Echo(s) ; }
function f(){} show('delete(f):',delete(f)) ; // false
The problem is I keep getting an error along the lines of: TypeError: Result of expression 'house' [[object Object]] is not a constructor. It seemed to work when I wasn't passing the other objects as parameters in the constructor. I just created and assigned them later. As in:
I'd like to make a Degree object that inherits from the Number object and uses the Number constructor but adds a .rad() method that returns the value in radians.
If I do something like:
It generally works but I don't get Number's methods like toString and toPrecision.
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.
I have static object and I want remake it to a constructor with property 'length' which would be not enumerable in for loop... This is my object and how I generate it
I have a setup where I need to get the function calling a function, which works fine, I just use arguments.callee.caller.Now I need to take it a step further and get the object that the function belongs too. For example in a onclick="parentObj.someFunction()" parentObj.someFunction calls some other function. I need a way to know that parentObj was involved, just getting someFunction isn't enough because parentObj has properties that are used in someFunction. To make it more interesting lets say I can't pass any more parameters to someFunction, so I can't pass parentObj into it as an argument.
I'm looking for a way to add more field depending on the user's input,. e.g. the user inputs ཆ' in the option, and 10 more sets of fields are displayed below on the same page. How do I go about accomplishing this?
I'm embarking on a rather interesting wine cellaring project where I need to enable a user to add form fields (a complete table row with several fields) on demand.
If they start filling out the form and need another row for another bottle, I need them to be able to click a button that adds a new row to the table with the same fields.
I also need perhaps another button that will create the row and duplicate the form field values of that row. The winery, wine namen and variety may be the same but the year may change and I dont wan thte user to have to do any double entry. I've been researching DOM and have been looking at sites like Quirksmode.
Am I heading in the right direction? I'm just about to go an buy a book on DOM and start really getting into it.
Javascript has a very small math function list. However there is no reason that this list can not be extended greatly. Speed is not an issue, unless you nest complicated calculations several levels deep. In that case you need much more ram than a PC has to store functions calculated in loops so that you do not have to recalculate every time you cycle through the nest of loops. Using a HD for storage to extend ram is much too slow for many applications.
Some functions such as hyperbolic ones are easy to add, since they are just simple combinations of the built in javascript math functions. I have found a few examples on the web such as Bessel functions. I found far fewer javascript math functions than I expected on Google searches. Thus I have had to write several functions of my own.
See http://www.cwdjr.net/math/I0L0andI1L1.html for an example of two "functions from hell" that are very difficult to evaluate. Fortunately there are Fortran programs that can be used as a starting point. I was able to modify the Fortran programs to work on javascript. I have used these functions for technical applications in the past.
The page is set up to reject the NN 4 series, because it will not support some of the script needed such as .toExponential(n) and to.Fixed(n)for writing output in exponential or fixed format. I was amazed that even the old MSNTV(former WebTV) set-top box, that no longer is being made, will even support these output formats. I wonder about IE4. If it will not support these output formats, I can easly block it by checking for document.getElementById.
The code works properly on the latest versions of IE6, MSN9, Firefox, Mozilla, Netscape, and Opera. I am not selling anything, so for a special interest page such as this, I see no need to support older browsers.
The advantage of doing math with javascript is that it is so portable. You can do it anywhere you can use a computer, or you can do it on your own local computer offline. There are several math programs for PCs that will do very much more than you can hope to do with javascript. Unfortunately the program I would like costs about US$ 1800. Also there are versions you can install on a server, but these also are expensive.
I am trying to create an HTML form in which user will enter different items (he wants to purchase) in text fields. One text field is used for one item. Now it is not known in advance how much items the user will purchase so we cannot decide the total text fields required in advance. Is is possible to increase the number of text fields (using JavaScript) one by one if the user requires more fields
How do I extend both the table and the input form? Ultimately, I want it to look like this: _____________________________ |header |header |header |header | | INPUT | INPUT | INPUT | INPUT | Add Row of Inputs Link _____________________________ |header |header |header |header | | INPUT | INPUT | INPUT | INPUT | | INPUT | INPUT | INPUT | INPUT | Add Row of Inputs Link
I know how to make the html row by using getElementById() or so and I know how to make an input field by createElement() but how do I create and append(?) them together, specifically the multiple input fields inside of the html row?
My website has demo music tracks and a Flash player. I've put the site in a frameset so that music continues to play while the user is browsing around.
The Flash player and menu are in a thin horizontal bar along the top of the page (top frame). I just realised that my nice JS drop-down menus are not displaying because of the frame... is there any way of getting them to extend beyond the frame they're contained in ?? Code:
var parent_child = function(po, ps, co, cs){ var url = 'http://xyz.com/abc/'; var pars = [], childs = {}, tmp; this.p_added = function(urlFrag){
[Code]....
What i want to do is to create a new class with the above one as the super class, pass in one more variable to the constructor and override the p_added function. I thought of doing something like xpc = new parent_child(); and override the function with xpc.prototype.p_added = function(){}
how to pass in another variable to the constructor and make it private to the new class.
I believe there is a nice and concise way to achieve what i want to, but i can't find it. And the fact that OOP in javascript can be implemented in several different ways doesn't help my cause.
