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JavaScript - Simulating Overloading Functions By Reassigning Reference And Using Anonymous Fnc
Similar TutorialsAm I doing something wrong here? I have two anonymous functions to validate two different forms on two different pages. They both work on the individual page, though when I try and put them in the same script.js folder only the top function seems to work. Code: <script type="text/javascript">
// Form Validation / Catalog Template ----------------------------------------------------------------------------------------------------------------------
document.getElementById("formValidation").onsubmit = function(){
if(document.getElementById("reqAddrCont").value == ""){
document.getElementById("reqAddrCont").className = "error";
return false;
}if(document.getElementById("reqAddrName").value == ""){
document.getElementById("reqAddrName").className = "error";
return false;
}if(document.getElementById("reqAddr1").value == ""){
document.getElementById("reqAddr1").className = "error";
return false;
}if(document.getElementById("reqAddr6").value == ""){
document.getElementById("reqAddr6").className = "error";
return false;
}if(document.getElementById("reqAddrState").value == "0"){
document.getElementById("reqAddrState").className = "error";
return false;
}if(document.getElementById("reqAddrPost").value == ""){
document.getElementById("reqAddrPost").className = "error";
return false;
}if(document.getElementById("reqAddrPhone").value == ""){
document.getElementById("reqAddrPhone").className = "error";
return false;
}if(document.getElementById("reqAddrEMail").value == ""){
document.getElementById("reqAddrEMail").className = "error";
return false;
}else{
return true;
}
};
// Form Validation / New Account Template --------------------------------------------------------------------------------------------------------------------------
document.getElementById("formValidationAccount").onsubmit = function(){
if(document.getElementById("AcctName").value == ""){
document.getElementById("AcctName").className = "error";
return false;
}if(document.getElementById("AcctTitle").value == ""){
document.getElementById("AcctTitle").className = "error";
return false;
}if(document.getElementById("AcctCompany").value == ""){
document.getElementById("AcctCompany").className = "error";
return false;
}if(document.getElementById("AcctAddress1").value == ""){
document.getElementById("AcctAddress1").className = "error";
return false;
}if(document.getElementById("AcctAddress2").value == ""){
document.getElementById("AcctAddress2").className = "error";
return false;
}if(document.getElementById("AcctAddress6").value == ""){
document.getElementById("AcctAddress6").className = "error";
return false;
}if(document.getElementById("AcctState").value == "0"){
document.getElementById("AcctState").className = "error";
return false;
}if(document.getElementById("AcctPost").value == ""){
document.getElementById("AcctPost").className = "error";
return false;
}if(document.getElementById("AcctCountry").value == ""){
document.getElementById("AcctCountry").className = "error";
return false;
}if(document.getElementById("AcctPhone").value == ""){
document.getElementById("AcctPhone").className = "error";
return false;
}if(document.getElementById("AcctLogin").value == ""){
document.getElementById("AcctLogin").className = "error";
return false;
}if(document.getElementById("AcctLogin2").value == ""){
document.getElementById("AcctLogin2").className = "error";
return false;
}if(document.getElementById("AcctPassword").value == ""){
document.getElementById("AcctPassword").className = "error";
return false;
}if(document.getElementById("AcctPasswordDupe").value == ""){
document.getElementById("AcctPasswordDupe").className = "error";
return false;
}else{
return true;
}
};
</script>
Hey all, I am confused about the true difference between the two below examples. Code: first example:
// Demonstrating a problem with closures and loops
var myArray = [“Apple”, “Car”, “Tree”, “Castle”];
var closureArray = new Array();
// Loop through myArray and create a closure for each that outputs that item
for (var i = 0; i < myArray.length; i++) {
var theItem = myArray[i];
closureArray[i] = function() {
document.write(theItem + “ < br / > ”);
}
}
// Loop through the closures and execute each one.
for (var i = 0; i < closureArray.length; i++) {
closureArray[i]();
}
Here we iterate through the length of myArray, assigning the current index of myArray to theItem variable. We declare closureArray 4 times as an anonymous function. The anonymous function in turn declares the predefined write() function, which is passed parameters. Since write() is in closureArray() a closure is created??? During each iteration, theItem is reassigned its value. The four closures reference this value. Since they reference this same value and since this value is reassigned ultimately to the value of the fourth index position, tHe time we execute closureArray later on, all four closures output the same string. This is because all four closures are within the same scope "the same environment" and therefore are referencing the same local variable, which has changed. I have a couple of problems with this example: 1) I thought a closure is a function that is returned - the inner function is not returned above. 2) theItem is not even a local variable of the parent function (closureArray) - I thought in order for a closure to work, the inner function only accesses the local variables of the outer function, but in this case the local variable is defined OUTSIDE of the parent function. 3) The guy says the "the four closures are sharing the same environment." The thing is even in the second example, they are sharing the same environment. Second example: Code: // A correct use of closures within loops
var myArray = [“Apple”, “Car”, “Tree”, “Castle”];
var closureArray = new Array();
function writeItem(word) {
return function() {
document.write(word + “ < br / > ”);
}
}
// Loop through myArray and create a closure for each that outputs that item
for (var i = 0; i < myArray.length; i++) {
var theItem = myArray[i];
closureArray[i] = writeItem(theItem);
}
// Loop through the closures and execute each one.
for (var i = 0; i < closureArray.length; i++) {
closureArray[i]();
}
Here we iterate over the length of myArray (4 times), assigning the index of myArray to theItem variable. We also return a function reference to the closureArray during each iteration (closureArray[i]), where i is index number so we assign 4 functon references. So when we iterate through myArray, we immediatelly call the writeItem() fucntion passing an argument of theItem at its current value. This returns a child anonymous function and when that child function is called, it will execute a block that calls the predefined write() method. We assign that returned anonymous function to the variable closureArray. Hence, closureArray holds a reference to that anonymous function. So closureArray during each iteration holds a reference to the anonymous function and we later call closureArray, which in turn calls the anonymous function, therefore calling the predefined write() function to output the local variable of the parent function. This outputs each distinct index of myArray. QUESTION: This is because since we created the closure, when we call writeItem, passing theItem argument, since theItem is a local variable of the parent function of the closure, it is never destroyed when we later call closureArray (the reference to the child anonymous function)? Yet weren't we using a closure in the first example as well? So whey wasn't those variables preserved? I don't think it has anything to do with assigning a returned anonymous function to closureArray. Even though an anonymous function creates a new memory position in the javascript engine, therefore not overwriting the other function references we create during the iteration, it's still referring to a local variable declared outside the reference. So if it's about the closure retaining value of parent's local variable even after exiting the parent function allowing for the current indexes to be preserved, then why did the closure in the first example fail to retain each index? Thanks for response I need to figure out a way to manipulate the arguments or functions or something somehow to have overloaded functions in JS. All I have found so far is people making like a switchboard function that directs the arguments based on the data, but not true overloading in that there is something like Function(input1) Function(input1,input2) Function(input1,input2,input3) And then you could call it with Function(x,y) or like Function(x,y,z) and hit the different functions. Any ideas? Edit: I was told to look at Functional Prototyping, which I understand the prototyping to be basiclly the parent from which others are made from. I don't see how it fits with overloading. Hey all, I am reading a book called JavaScript patterns. In it, this method is created: Code: var klass = function(Parent,template){
var Child, F, i;
Child = function () {
if (Child.uber && Child.uber.hasOwnProperty("__construct")) {
Child.uber.__construct.apply(this, arguments);
}
if (Child.prototype.hasOwnProperty("__construct")) {
Child.prototype.__construct.apply(this, arguments);
}
}
Parent = Parent || Object;
F = function () {};
F.prototype = Parent.prototype;
Child.prototype = new F();
Child.uber = Parent.prototype;
Child.prototype.constructor = Child;
for (i in template) {
if (template.hasOwnProperty(i)) {
Child.prototype[i] = template[i];
}
}
return Child;
}
Does anyone have an understanding of why we instantiate a new F() to the Child prototype rather than instantiate the Parent prototype? As you can see above, we assign Parent prototype to F prototype and then instantiate F() object to Child prototype. I'm not sure why it's being done this way. Code: F.prototype = Parent.prototype; Child.prototype = new F(); Thanks for response. I am trying to work out how to use Google Chrome DevTools to simulate a timeout on a JavaScript file on my site. I can use the 'Toggle Device Mode' to introduce throttling but that doesn't target a specific script. Is there a way to do this with DevTools? I am using Chrome 38. What I want to do is have a two-dimension array where some of the elements point to the value in another element. I have done this successfully in PHP using referfences (=&) and now I want to do it in JavaScript. My JS skills are limited but I found this post explaining how it can be done - http://stackoverflow.com/a/1687183 Here's the code from that - Code: Function.prototype.toString = function() {
return this();
}
var x = 1;
var y = function() { return x }
x++;
alert(y); // prints 2
It looks like it will do what I need to do. However, I want to use a two-dimension array, and if I try this it doesn't work - Code: for (var a = 2; a <= 5; a++)
for (var b = 1; b < a; b++)
matrix[a][b] = function() { return (matrix[b][a]) };
matrix is the two-dimension array which is alreay set up with some values. The two for loops are structured to fill in the rest of the values as references to existing values (it's a 5 x 5 array). The problem is coming from function() { return (matrix[b][a]) } because instead of the values for a and b being used in the creation of the anonymous function the actual variable names are used instead. Then later when I attempt to read one of the values setup by this it is "undefined" because the anonymous function is tries to return matrix[a][b] rather than matrix[4][2]. Can anyone help? Thanks! Hello, I'm hoping someone can help me with this. I have 3 pages that I need to put into my framework, they are products, shopping cart and billing. At the moment they work perfectly fine. Here is a live example - http://www.cems.uwe.ac.uk/~r4-george...g/products.php Now, I have a framework for a whole website that I need to put these pages into. (http://www.cems.uwe.ac.uk/~r4-george/wp4/index.php) The index uses a switch statement to go between pages. Here is the index.php PHP Code: <?php # index.php /* * This is the main page. * This page includes the configuration file, * the templates, and any content-specific modules. */ // Require the configuration file before any PHP code: require_once ('./modules/config.inc.php'); // Validate what page to show: if (isset($_GET['p'])) { $p = $_GET['p']; } elseif (isset($_POST['p'])) { // Forms $p = $_POST['p']; } else { $p = NULL; } // Determine what page to display: switch ($p) { case 'about': $page = 'about.inc.php'; $page_title = 'About This Site Again'; break; case 'products': $page = 'products.inc.php'; $page_title = 'Products on this site'; break; case 'this': $page = 'this.inc.php'; $page_title = 'This is Another Page.'; break; case 'that': $page = 'that.inc.php'; $page_title = 'That is Also a Page.'; break; case 'contact': $page = 'contact.inc.php'; $page_title = 'Contact Us'; break; case 'search': $page = 'search.inc.php'; $page_title = 'Search Results'; break; // Default is to include the main page. default: $page = 'main.inc.php'; $page_title = 'Site Home Page'; break; } // End of main switch. // Make sure the file exists: if (!file_exists('./modules/' . $page)) { $page = 'main.inc.php'; $page_title = 'Site Home Page'; } // Include the header file: include_once ('./includes/header.inc'); echo "<div id=\"content\">"; // Include the content-specific module: // $page is determined from the above switch. include ('./modules/' . $page); // Include the footer file to complete the template: include_once ('./includes/footer.inc'); ?> It uses the .inc.php files located in the modules folder to switch between pages. Here is my products.inc.php - PHP Code: <? include("includes/db.php"); include("includes/functions.php"); if($_REQUEST['command']=='add' && $_REQUEST['productid']>0){ $pid=$_REQUEST['productid']; addtocart($pid,1); header("location:shoppingcart.php"); exit(); } ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Products</title> <script language="javascript"> function addtocart(pid){ document.form1.productid.value=pid; document.form1.command.value='add'; document.form1.submit(); } </script> </head> <body> <form name="form1"> <input type="hidden" name="productid" /> <input type="hidden" name="command" /> </form> <div align="center"> <h1 align="center">Products</h1> <table border="0" cellpadding="2px" width="600px"> <? $result=mysql_query("select * from products"); while($row=mysql_fetch_array($result)){ ?> <tr> <td><img src="<?=$row['picture']?>" /></td> <td> <b><?=$row['name']?></b><br /> <?=$row['description']?><br /> Price:<big style="color:green"> £<?=$row['price']?></big><br /><br /> <input type="button" value="Add to Cart" onclick="addtocart(<?=$row['serial']?>)" /> </td> </tr> <tr><td colspan="2"><hr size="1" /></td> <? } ?> </table> </div> </body> </html> This is EXACTLY the same code as the working example. The products get listed correctly but the problem I have is the 'Add to Cart' button fails to work. Live example - http://www.cems.uwe.ac.uk/~r4-george...php?p=products Everything is in the right directory. When I inspect the 'Add to Cart' button in chrome I get the following - Quote: Uncaught TypeError: Cannot set property 'value' of undefined addtocart index.php:51 (anonymous function)index.php:83 onclick Any help is really appreciated, I'm struggling to see what I have done wrong. I don't know whether it's a Javascript problem. If you need any of the code from other pages I can post it too. Thanks in advance. I've been going through this great tutorial on how to implement a type-ahead feature on a text field and there's something which hopefully you guys can explain. On the third page there is this function. Code: AutoSuggestControl.prototype.init = function () {
var oThis = this;
this.textbox.onkeyup = function (oEvent) {
if (!oEvent) {
oEvent = window.event;
}
oThis.handleKeyUp(oEvent);
};
};
What I don't understand is this line: this.textbox.onkeyup = function (oEvent) { I know about anonymous functions, but I don't know where the value for the parameter oEvent is going to come from. Can someone explain this? Thanks! :) Hello! I'm working with nested functions and trying to pass a 'this' value to an anonymous being used in an assignment for an event listener. Here's the basics of my code: Code: <div id='abc'></div>
<script type='text/javascript'>
var abc = function () {
this.myFunction = function() {
var myObj
myObj = document.createElement("input");
myObj.setAttribute("type", "button");
myObj.setAttribute("value", "Click Me");
myObj.addEventListener("click", function () {
this.doDing();
}, false);
document.getElementById('abc').appendChild(myObj);
}
this.doDing = function () { alert('ding'); }
}
var myInstance = new abc();
myInstance.myFunction();
</script>
So, this should plop a button inside our DIV and when clicked I'd like it to run the alert-ding; unfortunately it seems to want to run the function as defined under the buttons object which doesn't work out too well. Any suggestions? Thanks! Hi, I have written a number of functions designed to return frequency data on 1000 randomly chosen numbers using different math functions for the rounding. I would like to include all of these functions within the wrapper of another function so that only one call is needed to get returns from all of the 'inner' functions. However, while each of the functions works in isolation, the moment I wrap them in another function they stop working. The following code is one of the functions 'frequencyWrapperOne' that has been wrapped in the function 'testWrapper'. A call to testWrapper does nothing. Can anyone see what I'm doing wrong? Code: function testWrapper()
{
function frequencyWrapperOne()
{
var numberArrayOne = new Array(0,0,0);
for (var i = 0; i < 1000; i = i + 1)
{
var chosenNumber = Math.floor(Math.random() * 3);
if (chosenNumber == 0)
{
numberArrayOne[0] = numberArrayOne[0] + 1;
}
if (chosenNumber == 1)
{
numberArrayOne[1] = numberArrayOne[1] + 1;
}
if (chosenNumber == 2)
{
numberArrayOne[2] = numberArrayOne[2] + 1;
}
}
return window.alert(numberArrayOne.join(','));
}
}
testWrapper();
Thanks. Hi All, I'm trying to convert an anonymous function to a real function (nesting is getting out of hand), however the msg object becomes undefined after conversion. Here is the converted anonymous function which fails: https://gist.github.com/2587613 and here is the original anonymous function which works: https://gist.github.com/2587667 Any help would be greatly appriciated Is there a way to activate a function from another function? It has to be in the script tag, it can't be in the HTML section. Can I use something similar to this following code? If not, can anyone give me some help? I have tried to do it various ways, and have looked it up a few times, but to no avail. Can I use something similar to this following code? If not, can anyone give me some help? if (condition) {activate functionname();} Any help I can get would be appreciated. Thanks a lot to anyone who can help. Ok here is what I have so far, my ending part of my Call Function I think is ok. for my main function. I think I misplaced the { and } I will show you all the codes I have for my main function this is what I have I think I did misplace something but I can not pin point where that one small things should be Code: unction showResults(race,name,party,votes)
{ // script element to display the results of a particular race
var totalV = totalVotes(votes);
document.write("<h2>" + race + "</h2>");
document.write("<table cellspacing='0'>");
document.write("<tr>");
document.write("<th>Candidate</th>");
document.write("<th class ='num'>Votes</th>");
document.write("<th class='num'>%</th>");
document.write("</tr>");
}
for (var i=0; i < name.length; i++)
{
document.write("<tr>");
document.write("<td>" name[i] + "(" + party[i] + ")</td>");
document.write("td class='num'>" + votes[i] + "</td>");
var percent=calcPercent(votes[i], totalV)
document.write("<td class='num'>(" + percent +"%)</td>");
createBar(party[i],percent)
document.write("</tr>");
}
document.write("</table>");
}
</script>
Just wondering if i misplaced any ; or { or } anywhere suggestions? Here is my call function Code: <script type="text/javascript"> showResults(race[0],name1,party1,votes1); showResults(race[1],name2,party2,votes2); showResults(race[2],name3,party3,votes3); showResults(race[3],name4,party4,votes4); showResults(race[4],name5,party5,votes5); </script> I been going over this, I can not seem to figure out what { i might be missing? Thanks Hi Experimenting. Trying to add a simple onclick event via onload, but I can't get it right? This works: Code: function checkStatus(box){
if(box.checked != box.defaultChecked){
alert("box status has changed");
}
}
HTML
<input type="checkbox" name="mycheckbox" id="mycheckbox" value="&cost=free" onclick="checkStatus(this)" />
This does not: Code: <input type="checkbox" name="mycheckbox" id="mycheckbox" value="&cost=free" />
window.onload = function (){
var mybox = document.getElementById('mycheckbox');
mybox.onclick = checkStatus ; //how to get this to work??
//none of the following work
//mybox.onclick = checkStatus; //this calls the function but I don't have a box ref
//mybox.onclick = checkStatus();
//mybox.onclick = checkStatus(this);
//mybox.onclick = checkStatus(mybox);
}
LT hey I want to get the href via attributes of this a tag & then this href to be set to a variable I'm working on making a searchable javascript and DOM reference...A chm like what php has. I mainly need it for myself because I don't always have access to the net. I was wondering if anyone would like to contribute? Hi! I'm working on a JSP based project. On myJsp1.jsp, I open a new window using window.open and store reference in a variable myWin like myWin = window.open(.........); from here i submit the form to myJsp2.jsp. In this file, I want the reference myWin to close the opened window. What I'm doing while submitting form is: myWin = window.open(.............); document.onlinePayStatusSummary.action ="myJsp2.jsp?action=forwardOnlinePayRequest&childWindow=" +myWin; document.onlinePayStatusSummary.submit(); I've read that this way JavaScript references can be passed in url. Now when I do getParameter in myJsp2.jsp as var winRef = "<%=request.getParameter("childWindow").toString()%>"; winRef.close(); I get JavaScript error that this winRef do not support the close() property. Any help? Hello, I'm working on a drag and drop HTML editor, in which blocks can be positioned. I need to build a controller which listens to mouse events and takes appropriate action (a state machine). The system is built using prototypes and objects. The Controller class looks like this (I removed some methods for simplification): Code: /**
* Creates a controller for a document
*/
function Controller() {
/**
* Document which is controlled by this controller
* @var Editor
* @access private
*/
this.document = null;
/**
* Overlay over the complete document, starting at the same position as the document
* @var HtmlElement
* @access private
*/
this.overlay = null;
/**
* References to event handlers
* @access private
*/
this.moveEventHandler = null;
/**
* Processes a mouse move in the viewport
* @param Controller reference Substitution for 'this'
* @param MouseEvent event
*/
this.handleMove = function(reference, event) {
//@do stuff
//Update selection region
reference.document.getSelection().setRange(..);
reference.document.getSelection().update();
return false;
}
/**
* Replaces the current document with the specified document
* @param Doc document
* @post Event handlers are ready to go
*/
this.setDocument = function(document) {
//Set document and overlay
this.document = document;
this.overlay = document.getOverlayContainer();
//Add event listeners to viewport
this.moveEventHandler = new EventHandler(this, this.handleMove);
if (this.overlay.addEventListener) {
//W3C browsers
this.overlay.addEventListener("mousemove", this.moveEventHandler, false);
} else if (this.overlay.attachEvent) {
//IE browsers
this.overlay.attachEvent("onmousemove", this.moveEventHandler);
}
//Disable right mouse menu and browser text selection
this.overlay.oncontextmenu = function() {return false;}
this.overlay.onselectstart = function() {return false;}
this.overlay.onmousedown = function() {return false;}
}
}
//Event handler wrapper
function EventHandler(reference, handler) {
this.reference = reference;
this.handler = handler;
this.handleEvent = function(e) {
this.handler(reference, e);
}
}
The method 'handleMove' is entitled to handle a mouse move on the overlay. Because the 'this' keyword would not point to the Controller object I've written a wrapper according to the W3C EventListener interface (http://www.w3.org/TR/DOM-Level-2-Eve...-EventListener). This wrapper holds a reference to the object in which the method resides that's handling the event, so that the important 'document' attribute can be reached. This document holds the document that is being edited (it's of a custom type, and not to be confused with the document as in document.body) The problem I now have is as follows. IE doesn't seem to be able to work with event handlers following the EventListener interface, but just functions. I need to get the object's reference there as well though, but this can't be done using an anonymous function, as at the moment it will be run it will be in a different scope, and not be able to reach the controller any more. Just using a global holding that reference variable, a method I used before, is not sufficient, as there may be multiple instances of the editor running on the same page. I have no problems in FFox, Opera, and Safari. Just IE because it uses an alternative event listener model. Has anyone got an idea how to get around this problem? Hi everyone, Does anybody know where I can download a decent Javascript reference in eBook format ?? Hey, I was having some trouble with this, and couldn't seem to find anything similar anywhere. (I'm not sure it's possible). (I know- for a normal variable there are no pointers in JS.) Normally, you can get an object reference: Code: obj.a = {...};
var pointer = obj.a;
//now, changes to pointer cause changes to obj.a
However, I would really like to be able to get a reference to a "variable" defined with a setter: Code: obj.__defineSetter__("a",function(input){...});
var pointer = obj.a;
//but now:
pointer = "..."; //does absolutely nothing! (as expected)
Anyone know a way to do this? (without using __defineSetter__ to create pointer). If you are wondering, this is what I would like to be able to do: Code: obj = {
a:function(value) {
obj.other=value;
this.__defineSetter__("a",function(input){
//do something with input, depending on obj.other
//reset obj.other
//reset obj.a to its original definition
});
return ? //return pointer to obj.a
}
}
obj.a("...") = OtherFunctionOutput();
obj.a("...2") = OtherFunctionOutput2();
//etc...
(This would be extremely useful in the context I'm working with. Basically, obj.a would be oscillating between a function that modifies some obj properties and a variable that can be set using cleaner syntax than is otherwise possible.) (The simple alternative would look like: ) Code: obj.a("...",OtherFunctionOutput());
(But, I'd really like to get the syntax described above working, if possible) Thanks for any help anyone! |
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