I was previously using the jQuery autosave plugin but have recently removed it. Some code is still trying to use this function, so how can I temporarily extend the jQuery object so there is an empty function to prevent errors until I can get through all of the code that is trying to use the function?
The plugin is called in this way:
jQuery().autosave.restore();
jQuery().autosave.save();
I think those are the only two functions that exist, so it would be OK to create two empty functions, but is there a way to create a catch-all function on this type of object?
Note
This is a temporary solution until I can go through a lot of code. I do believe the question is a valid coding question even if you think this workaround is not ideal (it isn't).
There is a way to do this. You can create a dummy plugin (check out jQuery's documentation for creating plugins):
(function( $ ){
$.fn.autosave = {
restore: function() {};
save: function() {};
};
})( jQuery );
I would highly recommend against doing this, however. Instead, you should look at those errors and fix them, i.e., stop your code from using them. Otherwise you're simply hiding the problem.
Nope. Standard JavaScript does not support "catch-all" methods.
Related
Excuse me first. because i don't know this is question is valid or not. i if any one clear my doubt then i am happy.
Basically : what is the different between calling a method like:
object.methodname();
$('#element').methodname();
calling both way is working, but what is the different between, in which criteria make first and second type of methods. is it available in the core javascript as well?
In case if i have a function is it possible to make 2 type of method call always?
Can any one give some good reference to understand correctly?
Thanks in advance.
The first syntax:
object.methodName();
Says to call a function, methodName(), that is defined as a property of object.
The second syntax:
$('#element').methodname();
Says to call a function called $() which (in order for this to work) must return an object and then call methodname() on that returned object.
You said that "calling both way is working," - so presumably you've got some code something like this:
var myObject = $('#element');
myObject.methodname();
This concept of storing the result of the $() function in a variable is commonly called "caching" the jQuery object, and is more efficient if you plan to call a lot of methods on that object because every time you call the jQuery $() function it creates another jQuery object.
"Is it available in the core javascript as well?" Yes, if you implement functions that return objects. That is, JS supports this (it would have to, since jQuery is just a JS library) but it doesn't happen automatically, you have to write appropriate function code. For example:
function getObject() {
return {
myMethod1 : function() { alert("myMethod1"); return this; },
myMethod2 : function() { alert("myMethod2"); return this; }
};
}
getObject().myMethod1().myMethod2();
In my opinion explaining this concept in more depth is beyond the scope of a Stack Overflow answer - you need to read some JavaScript tutorials. MDN's Working With Objects article is a good place to start once you have learned the JS fundamentals (it could be argued that working with objects is a JS fundamental, but obviously I mean even more fundamental stuff than that).
The difference is very subtle.
object.methodname();
This is when JavaScript has the object at hand.
$('#element').methodname();
If you are using jQuery, you are asking jQuery to select the object that has the id of #element. After that you invoke the method on the selected object.
Let's assume that we have following jQuery plugins (each of them in separate files):
$.fn.foo
$.fn.foo.bar
$.fn.foo.baz
I use standard jQuery plugin pattern. The first one is actually a proxy or "facade" to the rest plugins of it's namespace.
For example, when I call $('#el').foo(), under the hood I also call:
var context = this; // context is equal to $('#el')
$(context).foo['bar'].apply(context);
$(context).foo['baz'].apply(context);
There are two problem when I want to call only (without $.fn.foo) $('#el').foo.bar(). The first problem is that there are no $.fn.foo namespace but I can create it, so this is actually no problem. The second problem is that this inside $.fn.foo.bar is equal to document object but I want to be equal to $('#el'). How can I do that?
So, making a long story short, both should work:
$('#el').foo(); // This also calls foo.bar and foo.baz under the hood
$('#el').foo.bar(); // I'm calling foo.bar explicitly
I think you might just need to follow a different plugin pattern. Here is a nice repository of jQuery plugin patterns, but the one you might want to look at would be the namespace pattern - you'll see how the namespace gets defined initially if it doesn't already exist, and this allows you to more easily extend from a single namespace across multiple scripts.
Update: Hmm, I'm still learning so I wouldn't say I'm an expert at this, but trying to get this $('#el').aaa.bbb.ccc() to work got really messy for me. Maybe it would be better to not use that format, but instead do this (demo):
$.aaa.bbb.ccc( $("#el") );
because then it is relatively easy to set up:
(function() {
if (!$.aaa) {
$.aaa = {
bbb : {
ccc: function(el, options){
alert(el[0].id);
}
}
};
};
})(jQuery);
$(function() {
$.aaa.bbb.ccc( $("#el") ); // alerts "el"
});
Apologies for the vagueness of the title, I can't think of a succint way of summarising this question. I'm new to Javascript and JQuery and needed to respond to a checkbox being toggled, based on its value. Searching the site revealed lots of answers, mostly in the form:
$("input[type='checkbox']").click(function() {
if( $(this).is(':checked') ) {
//code here
}
})
In a flash of dynamic typing inspiration however, I tried typing this into my Javascript console:
$("input[type='checkbox']").click(function() {
if( this.checked ) {
//code here
}
})
...and to my surprise it worked! What's going on here behind the scenes? Is there a method defined called 'checked', or some kind of default property, or even a Ruby-style 'method missing' concept? Is this enabled by JQuery or is it intrinsic to Javascript?
It struck me as pretty awesome and I'd like to understand it better.
This basically boils down to the difference between this and $(this). (Read more here)
this is the DOM object for the current object where as $(this) is the jQuery wrapped version. This means you can do this.checked and is the same as calling normal Javascript.
What this does mean though is that, like #Val said you may run into cross browser issues as you are not relying on jQuery to solve these issues for you.
The reason it works is when the handler is called, its does something to the effect of:
callbackfn.call(<reference to event obj>, .. params .. )
If you go take a look at the JS reference, you'll see that the first parameter passed to .call is the context you want the function to run within. So in this case, since the object passed in is the clicked item, it will be the context.
I disagree with the other replies that this will cause you any trouble in xss browser compatibility, this is how you're supposed to do it and many many jQuery libraries rely on this.
See this stackoverflow article
$(this)[0] == this
Could someone write down a very simple basic example in javascript to conceptualize (and hopefully make me understand) how the jQuery plugin design pattern is done and how it works?
I'm not interested in how creating plugin for jQuery (so no jQuery code here at all).
I'm interested in a simple explanation (maybe with a bit of Javascript code) to explain how it is done the plugin concept.
Plz do not reply me to go and read jQuery code, I tried, but I it's too complex, otherwise I would have not post a question here.
Thanks!
jQuery has a library of functions stored in an internal object named fn. These are the ones that you can call on every jQuery object.
When you do $("div.someClass") you get a jQuery object containing all <div> elements of that class. Now you can do $("div.someClass").each( someFunction ) to apply someFunction to each of them. This means, that each() is one of the functions stored in fn (a built-in one in this case).
If you extend (add to) the internal fn object, then you automatically make available your custom function to the same syntax. Lets assume you have a function that logs all elements to the console, called log(). You could append this function to $.fn, and then use it as $("div.someClass").log().
Every function appended to the fn object will be called in such a way that inside the function body, the this keyword will point to the jQuery object you've used.
Common practice is to return this at the end of the custom function, so that method chaining does not break: $("div.someClass").log().each( someFunction ).
There are several ways to append functions to the $.fn object, some safer than others. A pretty safe one is to do:
jQuery.fn.extend({
foo: function() {
this.each( function() { console.log(this.tagName); } );
return this;
}
})
Tomalak already posted almost everything You need to know.
There is one last thing that helps jQuery do the trick with the this keyword.
it's amethod called apply()
var somefunction=function(){
alert(this.text);
}
var anObject={text:"hello"};
somefunction.apply(anObject);
//alert "hello" will happen
It really helps in creating abstractions so that framework/plugin users would just use this as intuition tells them, whatever there is inside Your code
It works, as many other js frameworks, using javascript prototype orientation.
For instance you can declare a simple function
var alertHelloWorld = function() {
alert('hello world');
}
And then tie it to an existing object (including DOM nodes)
document.doMyAlert = alertHelloWorld;
If you do this
document.doMyAlert();
The alertHelloWorld function will be executed
You can read more about javascript object prototyping here
I'm sure there are a million posts about this out there, but surprisingly I'm having trouble finding something.
I have a simple script where I want to set the onClick handler for an <A> link on initialization of the page.
When I run this I immediately get a 'foo' alert box where I expected to only get an alert when I click on the link.
What stupid thing am I doing wrong? (I've tried click= and onClick=)...
<script language="javascript">
function init(){
document.getElementById("foo").click = new function() { alert('foo'); };
}
</script>
<body onload="init()">
<a id="foo" href=#>Click to run foo</a>
</body>
Edit: I changed my accepted answer to a jQuery answer. The answer by 'Már Örlygsson' is technically the correct answer to my original question (click should be onclick and new should be removed) but I strongly discourage anyone from using 'document.getElementById(...) directly in their code - and to use jQuery instead.
Try:
document.getElementById("foo").onclick = function (){alert('foo');};
Use .onclick (all lowercase). Like so:
document.getElementById("foo").onclick = function () {
alert('foo'); // do your stuff
return false; // <-- to suppress the default link behaviour
};
Actually, you'll probably find yourself way better off using some good library (I recommend jQuery for several reasons) to get you up and running, and writing clean javascript.
Cross-browser (in)compatibilities are a right hell to deal with for anyone - let alone someone who's just starting.
jQuery:
$('#foo').click(function() { alert('foo'); });
Or if you don't want it to follow the link href:
$('#foo').click(function() { alert('foo'); return false; });
I tried more or less all of the other solutions the other day, but none of them worked for me until I tried this one:
var submitButton = document.getElementById('submitButton');
submitButton.setAttribute('onclick', 'alert("hello");');
As far as I can tell, it works perfectly.
If you want to pass variables from the current function, another way to do this is, for example:
document.getElementById("space1").onclick = new Function("lrgWithInfo('"+myVar+"')");
If you don't need to pass information from this function, it's just:
document.getElementById("space1").onclick = new Function("lrgWithInfo('13')");
OMG... It's not only a problem of "jQuery Library" and "getElementById".
Sure, jQuery helps us to put cross-browser problems aside, but using the traditional way without libraries can still work well, if you really understand JavaScript ENOUGH!!!
Both #Már Örlygsson and #Darryl Hein gave you good ALTARNATIVES(I'd say, they're just altarnatives, not anwsers), where the former used the traditional way, and the latter jQuery way. But do you really know the answer to your problem? What is wrong with your code?
First, .click is a jQuery way. If you want to use traditional way, use .onclick instead. Or I recommend you concentrating on learning to use jQuery only, in case of confusing. jQuery is a good tool to use without knowing DOM enough.
The second problem, also the critical one, new function(){} is a very bad syntax, or say it is a wrong syntax.
No matter whether you want to go with jQuery or without it, you need to clarify it.
There are 3 basic ways declaring function:
function name () {code}
... = function() {code} // known as anonymous function or function literal
... = new Function("code") // Function Object
Note that javascript is case-sensitive, so new function() is not a standard syntax of javascript. Browsers may misunderstand the meaning.
Thus your code can be modified using the second way as
= function(){alert();}
Or using the third way as
= new Function("alert();");
Elaborating on it, the second way works almost the same as the third way, and the second way is very common, while the third is rare. Both of your best answers use the second way.
However, the third way can do something that the second can't do, because of "runtime" and "compile time". I just hope you know new Function() can be useful sometimes. One day you meet problems using function(){}, don't forget new Function().
To understand more, you are recommended read << JavaScript: The Definitive Guide, 6th Edition >>, O'Reilly.
I agree that using jQuery is the best option. You should also avoid using body's onload function and use jQuery's ready function instead. As for the event listeners, they should be functions that take one argument:
document.getElementById("foo").onclick = function (event){alert('foo');};
or in jQuery:
$('#foo').click(function(event) { alert('foo'); }
Here is the YUI counterpart to the jQuery posts above.
<script>
YAHOO.util.Event.onDOMReady(function() {
document.getElementById("foo").onclick = function (){alert('foo');};
});
</script>
I think you want to use jQuery's .bind and .unBind methods. In my testing, changing the click event using .click and .onclick actually called the newly assigned event, resulting in a never-ending loop.
For example, if the events you are toggling between are hide() and unHide(), and clicking one switches the click event to the other, you would end up in a continuous loop. A better way would be to do this:
$(element).unbind().bind( 'click' , function(){ alert('!') } );
Nobody addressed the actual problem which was happening, to explain why the alert was issued.
This code: document.getElementById("foo").click = new function() { alert('foo'); }; assigns the click property of the #foo element to an empty object. The anonymous function in here is meant to initialize the object. I like to think of this type of function as a constructor. You put the alert in there, so it gets called because the function gets called immediately.
See this question.
The YUI example above should really be:
<script>
YAHOO.util.Event.onDOMReady(function() {
Dom.get("foo").onclick = function (){alert('foo');};
});
</script>