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JavaScript - Can I Override A Method, But Keep It's Scope?
I don't even know where to begin with this one.
I don't know the terminology for what I am trying to do here, and the sample code is too big and cluttered to post. So I put together the following to illustrate the structure of the object that I am trying to overcome. I have a method chain within an object, and I need to override one of the methods, but when I do so I loose access to the private methods and properties of it's containing object... I googled this for several hours, and the best that I can come up with is that I need to somehow use call() to access the scope of another object. But I don't understand call() or apply() at all, and I've read many tutorials on those... Code: window.oModule['Report'] = (function(){
var _privateProp1 = '' ,
_privateMethod1 = function(){
// ...
} ,
_publicMethod1 = function(){
// ...
} ,
_publicMethod2 = (function(){
var _sub_privateProp1 = '' ,
_sub_privateMethod1 = function(param1,param2){
// ...
} ,
_sub_publicMethod1 = function(){
// ...
} ,
_sub_publicMethod2 = function(start , end){ // I need to replace this method from somewhere else
var _neededValue = '';
for(var i = start ; i<end ; ++i) {
// ...
_neededValue += _sub_privateMethod1(arg1,arg2)
}
return _neededValue;
} ;
return{
'_sub_publicMethod1' : _sub_publicMethod1 ,
'_sub_publicMethod2' : _sub_publicMethod2
}
})() ;
return{
'_publicMethod1' : _publicMethod1 ,
'_publicMethod2' : _publicMethod2
}
})();
alert(oModule.Report._publicMethod2._sub_publicMethod2(1,5)) // This works fine
oModule.Report._publicMethod2._sub_publicMethod2 = function(start,end){ // Doing this modifies the output of all expressions that already call the sub method (which is what I need)
var _neededValue = '';
// ...
return start+end
}
alert(oModule.Report._publicMethod2._sub_publicMethod2(1,5)) // This will alert 6 (as intended)
oModule.Report._publicMethod2._sub_publicMethod2 = function(start,end){ // Doing this modifies the output of all expressions that already call the sub method (which is what I need)
var _neededValue = '';
for(var i = start ; i<end ; ++i) {
// ... different set of instructions
_neededValue += _sub_privateMethod1(arg1,arg2) // This line causes an error: _sub_privateMethod1 is undefined
}
return _neededValue
}
Similar TutorialsWhy is the callwhy is the slice method only a method of an Array instance? The reason why I ask is because if you want to use it for the arguments property of function object, or a string, or an object, or a number instance, you are forced to use Array.prototype.slice.call(). And by doing that, you can pass in any type of object instance (Array, Number, String, Object) into it. So why not just default it as a method of all object instances built into the language? In other words, instead of doing this: Code: function Core(){
var obj = {a : 'a', b : 'b'};
var num = 1;
var string = 'aff';
console.log(typeof arguments);//Object
console.log(arguments instanceof Array);//false
var args1 = Array.prototype.slice.call(arguments);
console.log(args1);
var args2 = Array.prototype.slice.call(obj);
console.log(args2);
var args3 = Array.prototype.slice.call(num);
console.log(args3);
var args4 = Array.prototype.slice.call(string);
console.log(args4);
Core('dom','event','ajax');
Why not just be able to do this: Code: function Core(){
var obj = {a : 'a', b : 'b'};
var num = 1;
var string = 'aff';
var args = arguments.slice(0);
var args2 = obj.slice(0);
var args3 = num.slice(0);
var args4 = string.slice(0);
//right now none of the above would work but it's more convenient than using the call alternative.
}
Core('dom','event','ajax');
Why did the designers of the javascript scripting language make this decision? Thanks for response. hi all ~ this is my code, when i change the first checkbox , i want to change the var theSame, but it seams doesn't change in if(theSame == 1) ; but it changes in alert("b"+theSame) , it's queer, how to handle this ? Code: <!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>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.0/jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
$(document).ready(function(){
var theSame = 1;
$("input[name='thesame']").change(function(){
theSame = $(this).is(":checked") ? 1 : 0;
alert("a"+theSame)
});
if(theSame == 1){
$(".check_list input").change(function(){
alert("b"+theSame)
});
}
});
</script>
</head>
<body>
<input type="checkbox" name="thesame">same
<br>
<div class="check_list">
<input type="checkbox" name="son">ppp
<input type="checkbox" name="son">ppp
<input type="checkbox" name="son">ppp
</div>
</body>
</html>
I have something like this var oneTest = new CustomObj({ prop1 : 'value1', prop2 : 'value2', prop3 : 'value3' }) var twoText = Object.clone(oneTest) twoText.prop2 = "newvalue2" And when I console log twoText I see something like +Data prop2 Inside Data is a prop2 that has the value of "value2". THAT is the one I want to change/override... yet the console shows me that the prop2 is outside of the data structure so when I am acting on the cloned obj I am not getting the results i need. I tried obj.extend etc.... and that didn't work, perhaps my syntax was wrong. Any advice? I am dynamically appending an img to the inner HTML of an element, to add in help in the form of a clickable icon next to select elements. When the img is added to an anchor the image of course becomes part of the link, and clicking the image invokes the anchor's action. The img has an onclick handler which triggers the dynamic help pop-up. My problem is that I can't seem to block the default anchor action, and thus the anchor is invoked also. The img onclick handler is called before the anchor event is processed (an alert popup will block the anchor's execution until the alert is dismissed), but returning false from it does not block the anchor's action. Any suggestions? I can move the img element to be a peer of the anchor element instead of a child, but I would like a programmatic fix instead of changing the way it interacts with the DOM if possible. Thanks. Hey all, I've built a website for my music and I'm fairly new to all this so bear with me. Essentially, I have two flash-based music players on my site. One is a simple single-track player that auto-plays some background music for the site. The functionality is limited to the user starting/stopping the music and adjusting the volume. The other is an advanced music player featuring a playlist of preselected tracks and allows the user to start/stop music, rewind, fast forward, adjust volume and select tracks in the playlist. This player does not start automatically. My question is this: when someone visits the site, the single-track background music player will start. Is there code that would allow the advanced music player, should it be turned on (i.e. someone selects a track and plays it), to override and actually stop the play of the single-track? TIA! Hi there - this seems like it should be an obvious problem - can anyone spot it? I have an object, declared this way: Code: var FK_gid = new picChooser('FK_gid', FK_gidArray);
FK_gid.init();
and a select group like this: Code: <select id = "FK_gid" name = "FK_gid"> <option value="none" selected="true" >None</option> <option value="335" >pics/zoobins.jpg</option> etc. etc. </select> picChooser in construction sets the onchange of the select group like this: Code: this.list = document.getElementById('FK_gid');
this.list.setAttribute("onchange", "FK_gid.displayImage();");
and the object's displayImage(); is like this: Code: this.displayImage = function () {
this.clearImage();
if (this.list.selectedIndex != 0)
{
pic = new Image();
pic.src = this.reformat(this.list.options[this.list.selectedIndex].innerHTML);
img = document.createElement("img");
img.src = pic.src;
this.preview.appendChild(img);
}
}
But whenever I choose something else off the list I get this error message: Code: TypeError: Result of expression 'FK_gid.displayImage' [undefined] is not a function. It's bizarre because when I type FK_gid.displayImage(); into Safari's dynamic console the function works perfectly... Any ideas? Thanks Edd I don't really understand why a.d() fails in the following, or rather why a.d can't access local vars in a, or how to rewrite this so that it can PHP Code: window.a = (function () { var b = '<br>hello '; var c = function (){ document.write(b+'from c') // in this scope we can access the local vars of a }; c() // this will work and write hello from c document.write(b) // this will work and write hello from b return{c:c} })(); a.d = function () { document.write(b+'from d') // even though as far as I can tell I have added d to the object a, } // this still can't access the local vars of a... why not? how can I change that? a.d() // doesn't work :( a.c() // this works too because we returned c in a's return statement I have a popup in one of my pages which is populated via AJAX call with a list of click-able options, this is all good, however I am now trying to display a javascript tree in the popup but it can not seem to 'see' the javascript routine that creates the tree, even if I hard code that into the popup itself, so the tree starts with d=new dTree() , and javasript is telling me that 'd' is undefined. the code works fine in a regular webpage but when pulled up in a AJAX generated popup it cant see squat? I tried parent.dTree() etc but to no avail. Is this because the javascript is loaded after the main page load via AJAX? if so is it accessible in anyway ? Hi all, I was looking at mozilla object.watch function and found this post http://stackoverflow.com/questions/1...r-all-browsers and the solution post has a object.watch function, my question is how is this implemented? Do I need to put it in a file and include it along with my other libs? When I call it do I need to add the .prototype or just PHP Code: myObject.watch("itemSelect", handler); Will this create a problem if I'm using mozilla? Thanks! I have devised the following constructor based loosely on the observer pattern Code: Observer = function (ConditionIsTrue , codeToExecute){
var
observer = this ,
ConditionWasMet = false ,
CheckIfReady = function () {
if (ConditionIsTrue()) {
if(!ConditionWasMet)
codeToExecute();
ConditionWasMet = true;
}
else {
if (ConditionWasMet) ConditionWasMet = false;
}
};
Loop.call(observer , CheckIfReady)
observer.speed(1)
};
It works fine, no problems that I know of... But the most interesting thing happened when I attached it to my lib and ran it through the http://closure-compiler.appspot.com/home compiler Code: $['Observer'] = function (//...etc... For the first time the compiler has added something to my global scope Code: var i=!1;
window.$=function(){//...etc...
...
Observer:function(j,k){var h=i;Loop.call(this,function(){j()?(h||k(),h=!0):h&&(h=i)});this.speed(1)}
}
})();
Can someone explain to me why the var ConditionWasMet had to be exported to the global scope? Was it already in the global scope? That would confuse me considering the observer can be called from multiple instances without conflict... But I don't want any surprise conflicts jumping out at me later, I appreciate the consideration. Let's say I'm defining an object and I want the constructor to take one input and ten save it. I'd like to do something like this: function apple(color) { this.color = arguments.color; } But of course that doesn't work because arguments isn't a scope. My question is, is there a scope I can use. What I've been doing instead is this: function apple(new_color) {this.color = new_color;} But that just seems less than perfectly pretty. I am doing project exercises from a JavaScript book for a college class. I am creating a brand new .html document for each project. I was under the impression that each unique page name would have its very own cookie scope. But to my surprise it seems adding/loading cookies using 'document.cookie' doesn't assign new cookies to each page. I am seeing that when I try to load document.cookie in new .html pages there are cookies that were already created in past pages in the document.cookie property/string. So whats the 'default' scope of a document cookie. Do I have to set the domain property to get unique cookies for each .html page I create? Thanks for the help. Edit: Okay, it seems that cookies have a default scope of the folder your .html page resides in and all sub-folders that your page resides in. I moved my project folder so that it was a sibling of my projects folder and it got its own cookies that way. Recently I had an issue while trying to copy an array: I couldn't understand why modifying the new array caused modifications in the old array Old Pedant cleared that up nicely for me in http://www.codingforums.com/showthread.php?t=240020 Now I'm trying to understand closures, and scope and all that fun stuff thanks to Venegal's great tutorial at reallifejs.com and I have the following: Code: <script>
window.USER = (function(){
var Employees = [['Alex',1,'ft',1],['Olivia',2,'ft',1],['Brenda',3,'ft',1],['Michael',4,'ft',1]];
var info = ['Start String'];
var Setup = function(){
}
return{
CheckLogin : function(login){
this.info = Employees[login];
},
Reset : function(){
},
info:info,
Emp:Employees
};
})();
</script>
And I think I got all the kinks worked out, but there was one thing that I don't understand... Based on my other thread I expected the modification of USER.info to overwrite values in USER.Emp Don't get me wrong, I didn't want that to happen, I am just confused as to why it didn't I used the following buttons to test the values of USER.info and USER.Emp but again, writing to USER.info did not overwrite anything in USER.Emp.... Code: <script>
document.write('<button onclick="alert(USER.info)">USER.info read</button>');
document.write('<button onclick="USER.info=\'Test String\'">USER.info write</button>');
document.write('<button onclick="alert(USER.Emp)">Employees read</button>');
document.write('<button onclick="USER.CheckLogin(0)">Check Login</button>');
</script>
So what I guess I'm asking is why? Or maybe: what is happening here, and how does it differ from my last issue? Was it maybe a scope issue? Or maybe something more sinister...? I am writing a rather large bookmarklet. For this bookmarklet I would like to have some user-defined variable values. My idea for this is a bookmarklet code something like this Code: var MY_var = "my value";
(function(){
/* usual loading of bookmarklet script file */
var s=document.createElement('script');
s.type='text/javascript';
s.src='https://myhost.com/path/to/my.js;
document.getElementsByTagName('head')[0].appendChild(s);
})();
However I can't access the variable MY_var in the bookmarklet script file "my.js". Is there any way I can change the bookmarklet so that I can access MY_var in my.js? This is a bit of a strange one. I have been trying to call a function in a child object from the parent object but the child seems to be going out of scope in onbeforeunload function. These function calls work outside of a onbeforeunload, so it only fails when called in onbeforeunload. I can fix it by making the child object a global but I was trying to avoid that. Anyone know why my childobject is out of scope when called in onbeforeunload? Notice I call that same function in windows onload event and it works fine. Here is the code (I have simplified as much as possible to just show the error): Code: <html>
<head>
<title>Broken Page</title>
<script language="javascript" type="text/javascript">
var myparent;
function windowLaunch()
{
myparent = new parent();
myparent.getchildvalue();
window.onbeforeunload = myparent.getchildvalue;
}
function parent()
{
this.mychild = new childobject("myinput");
this.getchildvalue = function()
{
var tmpval = this.mychild.returnvalue();
};
}
function childobject(thename)
{
this.myprop = thename;
this.returnvalue = function()
{
return (document.getElementById(this.myprop).value);
};
}
</script>
</head>
<body id="thebody" onload="windowLaunch();">
<div id="outerdiv">
<span title="This Input Box">My Input:</span><br />
<input id="myinput" style="width: 290px"/>
</div>
</body>
</html>
Hello, I am trying add some animation effects to a navigation button and am having some problems with my code. I am using setInterval(); and the problem came with trying to clear it using clearInterval(); if i have this code then it seems to clear it fine: Code:
var i = 21;
function w(){
document.getElementById("homebtntop").style.height = i + "px";
i--;
}
function c(){
if(i<=6){
window.clearInterval(t);
}
}
function r(){
t = self.setInterval("w()",15);
}
function slideIn(){
t = self.setInterval("w()",15);
clearInterval(t);
}
but if i then try to call it from inside a function c(); it doesn't work: Code: var i = 21;
function w(){
document.getElementById("homebtntop").style.height = i + "px";
i--;
}
function c(){
if(i<=6){
window.clearInterval(t);
}
}
function r(){
t = self.setInterval("w()",15);
}
function slideIn(){
t = self.setInterval("w()",15);
clearInterval(t);
}
Any ideas? i am sorry if my code makes no ssense or is badly formatted, this is my first time with javasript. Thank you. Question: if I declare a variable in on js fiile, is this available to another js file that is loaded? Answer: yes, it's available (unless inside of a function or something) BUT: does it matter WHERE I declare this variable?? Let's say, I have the following in my HTML file: <script src="script/main.js"></script> And then at the very bottom of my HTML page before the </body> tag I have: <script type="text/javascript">var myvariable = "Sample Data";</script> So, is myvariable available to main.js? In simple tests I've done, yes it does seem to be available But... what if I have a lot of other js code running in between Does this change anything? Thanks OM Hi all, I'm just starting out with Javascript as a development language and this will probably be a relatively simple problem for someone to solve for me. I am trying to access a variable (this.bodyEl.innerHTML) from within a function but get an error message indicating that it is "undefined". I know that it is a valid variable because I call it elsewhere outside of the inner function itself. I'm sure this is just a scope issue, but I'd welcome any suggestions on how to solve it with an explanation of where I've gone wrong if you have the time. Here's the code: Code: displayFeed: function(responseData) {
this.bodyEl.innerHTML = "xxxx"; // I can see this
var responseDoc = Presto.Util.parseXml(responseData);
var items = Ext.DomQuery.select("/rss/channel/item", responseDoc);
items.each(function(item, bodyHTML) {
var rssTitle = Ext.DomQuery.selectValue("/title", item);
var rssDescription = Ext.DomQuery.selectValue("/description", item);
var rssLink = Ext.DomQuery.selectValue("/link", item);
// but this results in an undefined error
this.bodyEl.innerHTML = '<a href="' + rssLink + '">' + rssTitle + '</a><br/>';
}); // end of items processing
}
This is a fragment of the code from my script. The first access of "this.bodyEl.innerHTML" works fine, but the second access in the items.each loop doesn't and I get an undefined variable error. Is this a scoping problem, and if so how is it best solved. Thanks in advance, Innes (NZ) First off... I am new to javascript, and am learning while trying to add some cool extra features to an existing project. An existing JSP is generating the HTML page and table. I have retro-fitted it so that it adds to each input field a 'trigger' to the onkeyup event. The purpose of this trigger is check for the the cursor keys being pressed (UP, DOWN, LEFT, RIGHT) and then if it is a logically valid move, shift to the next cell in that direction. Code: <td class="inputField" rowspan="1" colspan="1" nowrap="nowrap"> <input name="ColorNumber0" id="" maxlength="" size="20" onchange="saveFieldObj(this)" onkeyup="return doOnKeyUp(event, 18, 14, 'ColorNumber0')" type="text"> </td> Now, the function it calls, doOnKeyUp, for the most part is working fine... when the input field in the table cells are a textbox or textarea, my method can re-focus the fields appropriately. HOWEVER, I am having a huge headache when the input field is a combo box. Basically, the value of the combo box is changed with the cursor keys (which is default combo box behaviour (I think)), instead of moving to the next editable cell in that chosen direction. Problem #1: My question: Is there a way to intercept/override the various onKey events or similar for the combo boxes. For the combo boxes, I want to continue to move between table cells UNLESS a do something specific, like press the spacebar to entire an update/modification mode for the current cell. Everything I have done so far does not prevent the combo box events from triggering. Any ideas? Problem #2: Also, I tried a nasty hack to try and get it to work, by trying to switch the combo box's value back 1 spot (if it appeared to be needed) by changing the <combo box>.selected value. However, that change never appears to be taking hold, so it is staying at whatever the original selected value was. For this one, I am just curious as to the correct way to have javascript change the selected value in a combo box and make it "stick" and make it applied to the view/UI? Code example: Code: var selectedIdx = (curObj.selectedIndex - 0);
if ( selectedIdx < curObj.length ) {
var newIdx = (selectedIdx-0) - 1;
curObj[selectedIdx].selected = "0";
curObj[newIdx].selected = "1";
curObj[newIdx].focus();
//curObj.selectedIndex = newIdx;
}
You can probably tell by the code that I had been trying various things to change the combo box's selection via javascript, but none has worked for me. Any help on either topic would be greatly appreciated! Hey everyone, I wanted to write my own script for a fade-in animation, since the ones I have found have got too many options or need some framework, which makes them unnecessarily big. I wanted to learn too. Unfortunately, the code didn't work as I wanted, and I commented some things so as to find out what's happening. The only function called from outside is fadeIn with a string as argument (in the example, this string is: d1296668690535). This is the code: Code: var fadems = 500; // Anim. duration in milliseconds
var fps = 20; // Frames per second
function fadeIn(elemId){
var frames = fadems/1000 * fps;
var delay = 1000 / fps;
var incrOp = 1 / frames;
//document.getElementById(elemId).style.zoom = '1';
setOp(elemId, 0);
for(i=1; i<=frames; i++){
debugOutLn("(fadeIn for) elemId = " + elemId);
setTimeout("setOp(" + elemId + "," + incrOp*i + ")", delay*i);
}
}
function setOp(elemId, val){
debugOutLn("(setOp) elemId = " + elemId + "; val = " + val);
// document.getElementById(elemId).style.opacity = val;
// document.getElementById(elemId).style.filter = 'alpha(opacity = ' + val * 100 + ')';
}
Code: function debugOutLn(str){
document.getElementById("debug").innerHTML += str + "<br />";
}
And this is the text it outputs (on Opera 11.01): Code: (setOp) elemId = d1296668690535; val = 0 (fadeIn for) elemId = d1296668690535 (fadeIn for) elemId = d1296668690535 (fadeIn for) elemId = d1296668690535 (fadeIn for) elemId = d1296668690535 (fadeIn for) elemId = d1296668690535 (fadeIn for) elemId = d1296668690535 (fadeIn for) elemId = d1296668690535 (fadeIn for) elemId = d1296668690535 (fadeIn for) elemId = d1296668690535 (fadeIn for) elemId = d1296668690535 (setOp) elemId = [object HTMLDivElement] ; val = 0.1 (setOp) elemId = [object HTMLDivElement] ; val = 0.2 (setOp) elemId = [object HTMLDivElement] ; val = 0.30000000000000004 (setOp) elemId = [object HTMLDivElement] ; val = 0.4 (setOp) elemId = [object HTMLDivElement] ; val = 0.5 (setOp) elemId = [object HTMLDivElement] ; val = 0.6000000000000001 (setOp) elemId = [object HTMLDivElement] ; val = 0.7 (setOp) elemId = [object HTMLDivElement] ; val = 0.8 (setOp) elemId = [object HTMLDivElement] ; val = 0.9 (setOp) elemId = [object HTMLDivElement] ; val = 1 Why is an object reference assigned to what was previously a string? Thanks for the help! |
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