jQuery currently uses window as its default element so any call like $('div') will look for div tags inside window.
Is there any way to change defaults on jQuery like:
$.defaultRoot = $('.anyOtherRootElement');
$('div').text("Hello");
this will select any div inside the elements containing .anyOtherRootElement class.
Thanks in advance
Upate
just an update refining the question a bit more here:
I would like to perform the actions above based on external queries coming from external script which won't know what defaultRoot is so they can still be calling what is supposed to be the current base, so in this instance, I'm afraid adding the a second parameter wouldn't be an option, unfortunately.
And at the same time creating a function which returns defaultRoot.find(el) would prevent me of using first-level methods such $.trim, $.each, etc… so unfortunately that would not be possible as well.
Ideally (for performance reasons) you'd want to use find()
$.defaultRoot.find("div");
Otherwise you can use the 2 argument form that sets a context
$("div", $.defaultRoot);
In general you don't want to do these types of things implicitly since someone else could easily end up thoroughly confused when having to work with your code later. If you want to do it consistently and make it shorter you should create your own function to do so like:
var $s = function(selector) {
return $.defaultRoot.find(selector);
}
and then you'd just be able to use
$s("div")
or you could also do a scoped higher order function with something like
var withScope = function(scope$) {
return function(selector) {
return scope$.find(selector);
}
}
var $s = withScope($.defaultRoot);
$s("div")
If for some reason you really want to screw around with the default state for client code (begging for chaos IMO), you should look at the functional practice: currying.
$('SELECTOR', 'CONTEXT')
You can use context. As in your case $('div', '.anyOtherRootElement')
For more details, visit http://api.jquery.com/jQuery/
Given that you can pass the context as a second argument, you can easily overwrite the $() operator in Javascript with a version which internally calls JQuery using jQuery.noConflict(); and always passes your new root as the second argument.
I don't think jQuery provide such method or variable. But you can pass second parameter in jQuery method to set context.
$.defaultRoot = $('.anyOtherRootElement');
$('div', $.defaultRoot ).text("Hello"); // all div inside $('.anyOtherRootElement')
$('div' ).text("Hello"); //all div inside body tag
Let's say that our script is included in a web-page, and a prior script (that already executed) did this:
String.prototype.split = function () {
return 'U MAD BRO?';
};
So, the split string method has been overwritten.
We would like to use this method, so we need to recover it somehow. Of course, we could just define our own implementation of this method and use that instead. However, for the sake of this question, let's just say that we really wanted to recover the browser's implementation of that method.
So, the browser has an implementation of the split method (in native code, I believe), and this implementation is assigned to String.prototype.split whenever a new web-page is loaded.
We want that implementation! We want it back in String.prototype.split.
Now, I already came up with one solution - it's a hack, and it appears to be working, but it may have flaws, I would have to test a bit... So, in the meantime, can you come up with a solution to this problem?
var iframe = document.createElement("iframe");
document.documentElement.appendChild(iframe);
var _window = iframe.contentWindow;
String.prototype.split = _window.String.prototype.split;
document.documentElement.removeChild(iframe);
Use iframes to recover methods from host objects.
Note there are traps with this method.
"foo".split("") instanceof Array // false
"foo".split("") instanceof _window.Array // true
The best way to fix this is to not use instanceof, ever.
Also note that var _split = String.prototype.split as a <script> tag before the naughty script or not including the naughty script is obvouisly a far better solution.
I have just finished my script, using flot and jquery. Now to my question, it is fast in opera and Firefox, but it is painfully slow in internet explorer (no surprise), so thats why I wonder if there is a way to make my script more efficient (In other words perhaps remove some of the "for loops" etc)? So if there are any code gurus out there who have some spare time to kill, please help me out, because I myself am terrible at writing efficient code :P
Thanks so much in advance =)
It can be found
on this address
A few more tips:
It was pointed out that:
... $(this).attr('id');
... $(this).attr('name');
is expensive, you don't need $ here at all, just use:
... this.id;
... this.name;
Also, using .css(...) is a huge waste, use a class and put the CSS in an style element.
You can store references like $('#x') in closures. Again, you don't need $, it's far more efficient to get a reference directly to the element using document.getElementByid so that rather than:
$('#x').text(pos.x.toFixed(2));
you can have:
x.innerHTML = pos.x.toFixed(2);
which replaces several function calls with a single property access. The basic idea is to remove as much jQuery as you can, keep references to things rather than getting them frequently and use direct property access, not functions.
Incidentally, when I try to copy from the jsFiddle javascript region, Safari freezes. I'm not a big fan of that site.
for(k; k<datasets.length; k++){
Every time the loop is executed next, you are calling the length property, it's better if you store it in a variable at the start of the loop only, like this:
for(var k, len = datasets.length; k < len; k++){
Also here you are wasting resources:
key = $(this).attr("id");
subsystem = $(this).attr("name");
just stich $(this) into a variable, cause every time you use $() a clone of the passed element is created. Just do like this:
var $this = $(this);
And use $this from there on instead of $(this), only reuse $(this) when this become a different object.
Firstly, with jQuery selectors, if using a classname, it's more efficient if you can make that more specific. e.g instead of
var checkboxContainerFailed = $(".failedCheckboxes");
try
var checkboxContainerFailed = $("#graph-table-bottom td.failedCheckboxes");
Secondly, it's generally considered better to use [] notation instead of var subsystemNames = new Array();
Thirdly, you have a trailing comma in the data array here. This might cause IE problems:
"test2-a4/",
]
Finally, try running the whole thing through JSLint for any errors.
Currently I'm unit testing the following code:
if ($(selectedElement).innerText == 'blah')
{
// do something
}
with selectedElement being an anchor object selected from the UI.
In my test code, I have created a DOM structure which has that anchor in the proper position ready to be selected. The problem here is that since selectedElement is originally a javascript object, I need to convert the anchor I got from the DOM structure (which is a JQuery object) in order to get into the above condition.
I have tried the following, with no success:
// DOM structure using HtmlDoc
/*:DOC += <span id='testSpan' class='testSpanClass'><a href='#' id='selectedElem'>blah</a></span> */
selectedElement = $('#selectedElem')[0];
My goal is to be able to use a normal Javascript object to satisfy the condition, and also be able to switch it back to a jQuery object to satisfy conditions further down the function. But if there is a better approach I'll give it a go.
Does anyone have any ideas on how to go about this problem?
EDIT: Is there a solution that does not require changing of the code? selectedElement is actually a global variable.
Thanks.
I am not sure what browser you are testing in, but innerText is an IE only property. Since you are already using jQuery, I would suggest you just call the .text() method on the selected element like this:
selectedElement = $('#selectedElem')[0]; // Get DOM element
if ($(selectedElement).text() == 'blah')
{
// do something
}
You're method of getting the DOM object is fine: $('#selectedElem')[0] or $('#selectedElem').get(0) are equivalent, but the first one is faster in large loops.
jQuery's get method returns the original DOM elements for that jQuery object.
I think perhaps you need to use $('#selectedElem').get(0)
can you use jquery's .html() ?
if ($(selectedElement).html() == 'blah')
{
// do something
}
otherwise, without changing code:
var selectedElement = $('#selectedElem')[0];
if (selectedElement.innerHTML == 'blah')
{
// do something
}
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Closed 11 years ago.
I am starting a project with jQuery.
What pitfalls/errors/misconceptions/abuses/misuses did you have in your jQuery project?
Being unaware of the performance hit and overusing selectors instead of assigning them to local variables. For example:-
$('#button').click(function() {
$('#label').method();
$('#label').method2();
$('#label').css('background-color', 'red');
});
Rather than:-
$('#button').click(function() {
var $label = $('#label');
$label.method();
$label.method2();
$label.css('background-color', 'red');
});
Or even better with chaining:-
$('#button').click(function() {
$("#label").method().method2().css("background-color", "red");
});
I found this the enlightening moment when I realized how the call stacks work.
Edit: incorporated suggestions in comments.
Understand how to use context. Normally, a jQuery selector will search the whole doc:
// This will search whole doc for elements with class myClass
$('.myClass');
But you can speed things up by searching within a context:
var ct = $('#myContainer');
// This will search for elements with class myClass within the myContainer child elements
$('.myClass', ct);
Don't use bare class selectors, like this:
$('.button').click(function() { /* do something */ });
This will end up looking at every single element to see if it has a class of "button".
Instead, you can help it out, like:
$('span.button').click(function() { /* do something */ });
$('#userform .button').click(function() { /* do something */ });
I learned this last year from Rebecca Murphy's blog
Update - This answer was given over 2 years ago and is not correct for the current version of jQuery.
One of the comments includes a test to prove this.
There is also an updated version of the test that includes the version of jQuery at the time of this answer.
Try to split out anonymous functions so you can reuse them.
//Avoid
$('#div').click( function(){
//do something
});
//Do do
function divClickFn (){
//do something
}
$('#div').click( divClickFn );
Avoid abusing document ready.
Keep the document ready for initialize code only.
Always extract functions outside of the doc ready so they can be reused.
I have seen hundreds of lines of code inside the doc ready statement. Ugly, unreadable and impossible to maintain.
While using $.ajax function for Ajax requests to server, you should avoid using the complete event to process response data. It will fire whether the request was successful or not.
Rather than complete, use success.
See Ajax Events in the docs.
"Chaining" Animation-events with Callbacks.
Suppose you wanted to animate a paragraph vanishing upon clicking it. You also wanted to remove the element from the DOM afterwards. You may think you can simply chain the methods:
$("p").click(function(e) {
$(this).fadeOut("slow").remove();
});
In this example, .remove() will be called before .fadeOut() has completed, destroying your gradual-fading effect, and simply making the element vanish instantly. Instead, when you want to fire a command only upon finishing the previous, use the callback's:
$("p").click(function(e){
$(this).fadeOut("slow", function(){
$(this).remove();
});
});
The second parameter of .fadeOut() is an anonymous function that will run once the .fadeOut() animation has completed. This makes for a gradual fading, and a subsequent removal of the element.
If you bind() the same event multiple times it will fire multiple times . I usually always go unbind('click').bind('click') just to be safe
Don't abuse plug-ins.
Most of the times you'll only need the library and maybe the user interface. If you keep it simple your code will be maintainable in the long run. Not all plug-ins are supported and maintained, actually most are not. If you can mimic the functionality using core elements I strongly recommend it.
Plug-ins are easy to insert in your code, save you some time, but when you'll need an extra something, it is a bad idea to modify them, as you lose the possible updates. The time you save at the start you'll loose later on changing deprecated plug-ins.
Choose the plug-ins you use wisely.
Apart from library and user interface, I constantly use $.cookie , $.form, $.validate and thickbox. For the rest I mostly develop my own plug-ins.
Pitfall: Using loops instead of selectors.
If you find yourself reaching for the jQuery '.each' method to iterate over DOM elements, ask yourself if can use a selector to get the elements instead.
More information on jQuery selectors:
http://docs.jquery.com/Selectors
Pitfall: NOT using a tool like Firebug
Firebug was practically made for this kind of debugging. If you're going to be mucking about in the DOM with Javascript, you need a good tool like Firebug to give you visibility.
More information on Firebug:
http://getfirebug.com/
Other great ideas are in this episode of the Polymorphic Podcast:
(jQuery Secrets with Dave Ward)
http://polymorphicpodcast.com/shows/jquery/
Misunderstanding of using this identifier in the right context. For instance:
$( "#first_element").click( function( event)
{
$(this).method( ); //referring to first_element
$(".listOfElements").each( function()
{
$(this).someMethod( ); // here 'this' is not referring first_element anymore.
})
});
And here one of the samples how you can solve it:
$( "#first_element").click( function( event)
{
$(this).method( ); //referring to first_element
var $that = this;
$(".listOfElements").each( function()
{
$that.someMethod( ); // here 'that' is referring to first_element still.
})
});
Avoid searching through the entire DOM several times. This is something that really can delay your script.
Bad:
$(".aclass").this();
$(".aclass").that();
...
Good:
$(".aclass").this().that();
Bad:
$("#form .text").this();
$("#form .int").that();
$("#form .choice").method();
Good:
$("#form")
.find(".text").this().end()
.find(".int").that().end()
.find(".choice").method();
Always cache $(this) to a meaningful variable
especially in a .each()
Like this
$(selector).each(function () {
var eachOf_X_loop = $(this);
})
Similar to what Repo Man said, but not quite.
When developing ASP.NET winforms, I often do
$('<%= Label1.ClientID %>');
forgetting the # sign. The correct form is
$('#<%= Label1.ClientID %>');
Events
$("selector").html($("another-selector").html());
doesn't clone any of the events - you have to rebind them all.
As per JP's comment - clone() does rebind the events if you pass true.
Avoid multiple creation of the same jQuery objects
//Avoid
function someFunc(){
$(this).fadeIn();
$(this).fadeIn();
}
//Cache the obj
function someFunc(){
var $this = $(this).fadeIn();
$this.fadeIn();
}
I say this for JavaScript as well, but jQuery, JavaScript should NEVER replace CSS.
Also, make sure the site is usable for someone with JavaScript turned off (not as relevant today as back in the day, but always nice to have a fully usable site).
Making too many DOM manipulations. While the .html(), .append(), .prepend(), etc. methods are great, due to the way browsers render and re-render pages, using them too often will cause slowdowns. It's often better to create the html as a string, and to include it into the DOM once, rather than changing the DOM multiple times.
Instead of:
var $parent = $('#parent');
var iterations = 10;
for (var i = 0; i < iterations; i++){
var $div = $('<div class="foo-' + i + '" />');
$parent.append($div);
}
Try this:
var $parent = $('#parent');
var iterations = 10;
var html = '';
for (var i = 0; i < iterations; i++){
html += '<div class="foo-' + i + '"></div>';
}
$parent.append(html);
Or even this ($wrapper is a newly created element that hasn't been injected to the DOM yet. Appending nodes to this wrapper div does not cause slowdowns, and at the end we append $wrapper to $parent, using only one DOM manipulation):
var $parent = $('#parent');
var $wrapper = $('<div class="wrapper" />');
var iterations = 10;
for (var i = 0; i < iterations; i++){
var $div = $('<div class="foo-' + i + '" />');
$wrapper.append($div);
}
$parent.append($wrapper);
Using ClientID to get the "real" id of the control in ASP.NET projects.
jQuery('#<%=myLabel.ClientID%>');
Also, if you are using jQuery inside SharePoint you must call jQuery.noConflict().
Passing IDs instead of jQuery objects to functions:
myFunc = function(id) { // wrong!
var selector = $("#" + id);
selector.doStuff();
}
myFunc("someId");
Passing a wrapped set is far more flexible:
myFunc = function(elements) {
elements.doStuff();
}
myFunc($("#someId")); // or myFunc($(".someClass")); etc.
Excessive use of chaining.
See this:
this.buttonNext[n ? 'bind' : 'unbind'](this.options.buttonNextEvent, this.funcNext)[n ? 'removeClass' : 'addClass'](this.className('jcarousel-next-disabled')).attr('disabled', n ? false : true);
Explanation
Use strings accumulator-style
Using + operator a new string is created in memory and the concatenated value is assigned to it. Only after this the result is assigned to a variable.
To avoid the intermediate variable for concatenation result, you can directly assign the result using += operator.
Slow:
a += 'x' + 'y';
Faster:
a += 'x';
a += 'y';
Primitive operations can be faster than function calls
Consider using alternative primitive operation over function calls in performance critical loops and functions.
Slow:
var min = Math.min(a, b);
arr.push(val);
Faster:
var min = a < b ? a : b;
arr[arr.length] = val;
Read More at JavaScript Performance Best Practices
If you want users to see html entities in their browser, use 'html' instead of 'text' to inject a Unicode string, like:
$('p').html("Your Unicode string")
my two cents)
Usually, working with jquery means you don't have to worry about DOM elements actual all the time. You can write something like this - $('div.mine').addClass('someClass').bind('click', function(){alert('lalala')}) - and this code will execute without throwing any errors.
In some cases this is useful, in some cases - not at all, but it is a fact that jquery tends to be, well, empty-matches-friendly. Yet, replaceWith will throw an error if one tries to use it with an element which doesn't belong to the document. I find it rather counter-intuitive.
Another pitfall is, in my opinion, the order of nodes returned by prevAll() method - $('<div><span class="A"/><span class="B"/><span class="C"/><span class="D"/></div>').find('span:last-child').prevAll(). Not a big deal, actually, but we should keep in mind this fact.
If you plan to Ajax in lots of data, like say, 1500 rows of a table with 20 columns, then don't even think of using jQuery to insert that data into your HTML. Use plain JavaScript. jQuery will be too slow on slower machines.
Also, half the time jQuery will do things that will cause it to be slower, like trying to parse script tags in the incoming HTML, and deal with browser quirks. If you want fast insertion speed, stick with plain JavaScript.
Using jQuery in a small project that can be completed with just a couple of lines of ordinary JavaScript.
Not understanding event binding. JavaScript and jQuery work differently.
By popular demand, an example:
In jQuery:
$("#someLink").click(function(){//do something});
Without jQuery:
<a id="someLink" href="page.html" onClick="SomeClickFunction(this)">Link</a>
<script type="text/javascript">
SomeClickFunction(item){
//do something
}
</script>
Basically the hooks required for JavaScript are no longer necessary. I.e. use inline markup (onClick, etc) because you can simply use the ID's and classes that a developer would normally leverage for CSS purposes.