1) is getRule a local variable or global variable, as it has no var keyword, yet it is an inner function of Validation? So without var, I think global, but being an inner function, I think local. So I'm not sure which.
2) In this line of code: var rule = $.Validation.getRule(types[type]), getRule returns rules, which is just a local variable in Validation. I always see that you return functions, but how does returning a local variable that's just an object literal and not a function be able to return true or false? Now the value of rules is an object literal, and this object returns true or false. So we are basically allowed to use return keyword with local variables that are object literals and not functions?
3) In this line, is foo(age) being called, or is it just being assigned to bar OR is it being called and THEN assigned to bar: var bar = foo(age);
4) Now for the most confusing: age is obviously an object reference as opposed to a literal in the example. Does that make a difference in regards to closures?
Note that I read a number of books, including JavaScript Programmer Reference and Object Oriented JavaScript and jQuery cookbook, which compare primitives vs reference types and how primitive types store directly in memory whereas reference tpyes reference memory, so if one reference changes, they all change where primitive remains ingrained. But when assigning a function as a reference like this, how does that affect the object "age" when passed into bar?
Code:
function foo(x) {
var tmp = 3;
return function (y) {
alert(x + y + tmp);
x.memb = x.memb ? x.memb + 1 : 1;
alert(x.memb);
}}
var age = new Number(2);
var bar = foo(age); // bar is now a closure referencing age.
bar(10);
I am confused about the true difference between the two below examples.
first example:
// Demonstrating a problem with closures and loops var myArray = [“Apple”, “Car”, “Tree”, “Castle”]; var closureArray = new Array();
[code]....
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 "the four closures are sharing the same environment." The thing is even in the second example, they are sharing the same environment.
Second example:
// A correct use of closures within loops var myArray = [“Apple”, “Car”, “Tree”, “Castle”]; var closureArray = new Array();
[code]....
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.
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?
I am a bit new to JavaScript objects, I have the following object:
LinkTest=function() { // init }
LinkTest.prototype.eventHandler=function(){ // the call below fails, as 'this' refers to the link that // generated the event, and not the instance of LinkTest object this.doSomething(); }
LinkTest.prototype.doSomething=function() { // do something! }
So basically when you register a link, the onclick event handler gets a reference to LinkTest's eventHandler function. Now when the user clicks on the link, the 'this' refers to the link... how do I reference the instance of LinkTest object from within the eventHandler function?
I want to be able to set a property on a private object by giving the not notation path to the value. The difficulty is that this object is within closure so I can't access it directly to set the value the normal way (eg. dot.notation.path = 'new value'). This seems weird but I can't think of the obvious way.
Example:
// setter function function set(path, change){ var privateObject = { a: 'a',
I am trying to make a function that checks/unchecks a checkbox when a specific <td> is clicked. I need to use this same function for several checkboxes in the page so I want to just pass it the name of the checkbox I want to affect as a variable and use it in the object reference lines. BUT, this doesn't work. I can pass the variable to the function as I've used alert(variable) to test this. But it doesn't work when I put it in a line like this "document.forms[0].variable.checked=true;". Code:
THE QUESTION: How do I get a reference to my Object when processing an event handler bound to an html element ?
CONTEXT: Sorry if it is a bit long.
I am developing a JS calendar tool. One of the requirements is that the calendar will need to display a varying number of months (1..3) depending on the calling page. Imagine 1, 2 or 3 calendar pages side by side as required.
I have built a grid object that will contain one month's dates with the day names at the top. The calendar object inherits the grid object as an array of "calendar pages" - one grid per month and the calendar provides the content for each grid. I will use the grid object for another completely different object later and so I want to use good OOP encapsulation. The grid is a table generated on the fly and is "dumb" as far as what it is used for.
I have attached an onlick event to each cell of the grid. Using OOP priciples I want the calling program (the calendar object in this case) to provide a function to handle the click and the grid object will provide to the calendar the row and column of that cell as well as the grid number (so the calendar can work out which date was clicked since it knows what the data means and the grid doesnt). Code:
I'm not sure why, but the Console.focus() and Console.writeln() methods just don't seem to be able to use the DOM references stored in Console.STDIN and Console.STDOUT. Everything's fine in the constructor, but other methods can't seem to use them.
Is it possible to test whether two objects are equal using the data they contain inside and not comparing their pointers with ==?
Well actually of course there is but...
Is there a way to do it without actually looping through the object, instead maybe something that came with JS? (something like a .equals() method from other programming languages.)
Can assign a new function to a built-in object in Firefox:
But IE and Opera don't have a MouseEvent or HTMLElement that can be set up in the same way. Can you do this in IE or Opera, or just Firefox, and maybe Webkit?
I'm using the standard module pattern and the problem is once you set a private variable, trying to test that object independently becomes a nightmare as the next test is polluted by the actions of the previous.So, the options are to have some reset method (which is horrible), setters on everything (defeats the point) or delete object and re-load script (hideous).
I have a javascript function that needs to access methods of a java object(localTag). In my JSP I'm trying to include hidden fields for the Strings returned from the getter method calls of the object like so:
If I can do something like this, what is the correct syntax and how do I access this property in my javascript? When I have a hidden field that is just a String, I access it in the javascript like "document.getElementById("theString").value" and it works fine, but I can't seem to find how to access the String value of a method call.
When you use addEventListener (or addEvent in IE) to call an object method, does it call it with the correct this parameter?
The ECMAScript reference has a lot to say about the caller using Function.prototype.call or Function.prototype.apply and passing the correct this pointer for the context, but how does addEventListener determine the correct this pointer. Or does it just punt and pass the global context, thus making it impossible to refer to the object this in an object method used as an event listener?
I have more of a programme design related question here: I have an object with 2 methods, those two methods are supposed to be called repeatedly one after the other (e.g. by setInterval())
the problem with this code is that the execution time of those methods may increase depending on the processed data (an array with several hundred elements or more) so it may be, that the execution time of both methods exceeds the given repetition time. I could solve that by placing a call to the next function in each method, but I wonder if that is good design or not (tight coupling)
code for method2() is analogue Obj.prototype.method1 = function () { /* working code here */
When a custom object is created in javascript, then methods need to be defined for this object. Still every object has toString() method available to them, even if it is not defined. How is this method available to all the objects ? Is it inherited from some root object ?
Is sort() method available to all the objects ? What are the other methiods available to all objects ? Where can I get list of available methods ?
I am a little confused how the memory for objects is allocated in JavaScript. David Flanagan, in "javascript: The Definitive Guide," states that each property of a class takes up memory space when instantiated. So space is created for aMethod three times in this example: Code:
Do many programmers remember most of the object properties and methods or do they use IDE or references to find those specific objects. I'm starting to learn Javascript and seeing all the different type of objects available can be depressing. :(
Well, I've been working with JS for three years and have a great experience here. But! I still have no really acceptable answer to the following question:
What is the principle difference between declaring methods/properties in the constructor function body and via prototypes.
Are there any real GURUs? Let's discuss the issue.
I'm attempting to understand the use of privileged methods when used with Object.create. I put together a quick demo (code below) that shows what happens when I use Object.create to create a new object based on one that has a privileged method. The outcome is not pleasant, as changing the value in the first object also changes it in the second. Unless I am reading Crockford's articles incorrectly, this makes Object.create almost useless for anything but objects that have only public members.
I've seen many JavaScript programmers use closures extensively to create private members, and that still holds to be a good programming practice. However I still can't find an elegant way to create inheritance in combination with closures in JavaScript, given downfalls such as the one I mentioned above.With all of that said I still think Crockford has a nice way of programming, creating factory functions that produce objects, staying away from the prototype property and making the language look more functional.
Here's the code to demonstrate what I'm referring to. Firebug needs to be enabled to view the console.debug output, otherwise convert them to alerts.
if (typeof Object.create !== 'function') { Object.create = function (o) { function F() {}
I have an object on the document element that allows for other components to register with it, i have a custom event something along$(document).bind("register",function(thechild)..So in the child object when they are created i call$(document).trigger("register",this);And indeed i get the DOM object. However i'm looking for the plug in object, i want to be able to call methods on the passed childobject and access it's Config.Does that make sense? How can i write a plug in that is applied to various objects that also registers itself with an 'overseer' object on the document element in such a way that i can allow that overseer object to call methods on any registered child objects?
Arg, I'm losing hair. I'm having trouble understanding something extremely basic and important. I have functions who call functions who call functions.. but I'm having trouble doing anything useful with their results. I can't seem to "grab" them. They just get garbage collected. Scope is becoming my enemy.
This is also hard to explain because the code is modular, so stuff is calling stuff is calling stuff.
Everything happens inside a large Object.
[Code]...
Where do I have to go to understand basic Javascript things like getting values back out of a function? It's always the same problem I hit every time I use functions to figure out some value. It's always locked away.
If anyone happens to know of some place where one can practice with these things, that would be nice.Closures for morons? Functions for dummies? Something like that. I've got bookmarks of pages explaining functions and values and closures but I can't seem to take that over to what I want to do with them.
function attributes() { var attr1 = arguments[0] || '_' var attr2 = arguments[1] || '_' return ( function (el1, el2) { var value1 = el1[attr1] + el1[attr2]; var value2 = el2[attr1] + el2[attr2]; if (value1 > value2) return 1; else if (value1 < value2) return -1; else return 0; } ); }
var a = [ { a:'smith', b:'john' }, { a:'jones', b:'bob' }, { a:'smith', b:'jane' } ]; a.sort(attributes('a', 'b')); for (var i =0; i < a.length; i++) { document.write(a[i].a + ', ' + a[i].b + '<br>'); }
My question is, are attr1 and attr2 guaranteed to exist through the lifetime of a.sort(attributes('a', 'b'))?
As I understand it, the anonymous inner function reference I am returning is a property of attributes(). As such, when I return a reference to the anonymous inner function, the outer attributes() function must continue to exist (as must attr1 and att2) until there are no further references to the inner anonymous function.
As a result, there is no danger of attr1 or attr2 "disappearing" during the repeated calling of the anonymous inner function.
Is my explanation basically correct, or am I deluding myself and I'm just lucky that the garbage collector hasn't recovered attr1 or attr2 while the sort is still going on? In other words, is the behaviour I'm seeing consistent and predictable, or should I change my approach?