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jquery interview questions

Top jquery frequently asked interview questions

event.preventDefault() vs. return false

When I want to prevent other event handlers from executing after a certain event is fired, I can use one of two techniques. I'll use jQuery in the examples, but this applies to plain-JS as well:

1. event.preventDefault()

$('a').click(function (e) {
    // custom handling here
    e.preventDefault();
});

2. return false

$('a').click(function () {
    // custom handling here
    return false;
});

Is there any significant difference between those two methods of stopping event propagation?

For me, return false; is simpler, shorter and probably less error prone than executing a method. With the method, you have to remember about correct casing, parenthesis, etc.

Also, I have to define the first parameter in callback to be able to call the method. Perhaps, there are some reasons why I should avoid doing it like this and use preventDefault instead? What's the better way?


Source: (StackOverflow)

How can I upload files asynchronously?

I would like to upload a file asynchronously with jQuery. This is my HTML:

<span>File</span>
<input type="file" id="file" name="file" size="10"/>
<input id="uploadbutton" type="button" value="Upload"/>

And here my Jquery code:

$(document).ready(function () {
    $("#uploadbutton").click(function () {
        var filename = $("#file").val();

        $.ajax({
            type: "POST",
            url: "addFile.do",
            enctype: 'multipart/form-data',
            data: {
                file: filename
            },
            success: function () {
                alert("Data Uploaded: ");
            }
        });
    });
});

Instead of the file being uploaded, I am only getting the filename. What can I do to fix this problem?

Current Solution

I am using the jQuery Form Plugin to upload files.


Source: (StackOverflow)

jQuery document.createElement equivalent?

I'm refactoring some old JavaScript code and there's a lot of DOM manipulation going on.

var d = document;
var odv = d.createElement("div");
odv.style.display = "none";
this.OuterDiv = odv;

var t = d.createElement("table");
t.cellSpacing = 0;
t.className = "text";
odv.appendChild(t);

I would like to know if there is a better way to do this using jQuery. I've been experimenting with:

var odv = $.create("div");
$.append(odv);
// And many more

But I'm not sure if this is any better.


Source: (StackOverflow)

Is Safari on iOS 6 caching $.ajax results?

Since the upgrade to iOS 6, we are seeing Safari's web view take the liberty of caching $.ajax calls. This is in the context of a PhoneGap application so it is using the Safari WebView. Our $.ajax calls are POST methods and we have cache set to false {cache:false}, but still this is happening. We tried manually adding a TimeStamp to the headers but it did not help.

We did more research and found that Safari is only returning cached results for web services that have a function signature that is static and does not change from call to call. For instance, imagine a function called something like:

getNewRecordID(intRecordType)

This function receives the same input parameters over and over again, but the data it returns should be different every time.

Must be in Apple's haste to make iOS 6 zip along impressively they got too happy with the cache settings. Has anyone else seen this behavior on iOS 6? If so, what exactly is causing it?


The workaround that we found was to modify the function signature to be something like this:

getNewRecordID(intRecordType, strTimestamp)

and then always pass in a TimeStamp parameter as well, and just discard that value on the server side. This works around the issue. I hope this helps some other poor soul who spends 15 hours on this issue like I did!


Source: (StackOverflow)

jQuery's jquery-1.10.2.min.map is triggering a 404 (Not Found)

I'm seeing error messages about a file, min.map, being not found:

GET jQuery's jquery-1.10.2.min.map is triggering a 404 (Not Found)


Screenshot

enter image description here

Where is this coming from?


Source: (StackOverflow)

How can I select an element with multiple classes?

I want to select all the elements that have the two classes a and b.

<element class="a b">

So, only the elements that have both classes.

When I use $(".a, .b") it gives me the union, but I want the intersection.


Source: (StackOverflow)

How can I refresh a page with jQuery?

How can I refresh a page with jQuery?


Source: (StackOverflow)

Disable/enable an input with jQuery?

$input.disabled = true;

or

$input.disabled = "disabled";

Which is the standard way? And, conversely, how do you enable a disabled input?


Source: (StackOverflow)

$(document).ready equivalent without jQuery

I have a script that uses $(document).ready, but doesn't use anything else from jQuery. I'd like to lighten it up by removing the jQuery dependency.

How can I implement my own $(document).ready functionality without using jQuery? I know that using window.onload will not be the same, as window.onload fires after all images, frames etc have been loaded.


Source: (StackOverflow)

Creating a div element in jQuery

How do I create a div element in jQuery?


Source: (StackOverflow)

How to move an element into another element?

I would like to move one DIV element inside another. For example, I want to move this (including all children):

<div id="source">
...
</div>

into this:

<div id="destination">
...
</div>

so that I have this:

<div id="destination">
  <div id="source">
    ...
  </div>
</div>

Source: (StackOverflow)

How do I insert an Item into an array at a specific Index?

I am looking for a Javascript array insert method, in the style of:

arr.insert(index, item)

Preferably in jQuery, but any Javascript implementation will do at this point.


Source: (StackOverflow)

Convert form data to JavaScript object with jQuery

How do I convert all elements of my form to a JavaScript object?

I'd like to have some way of automatically building a JavaScript object from my form, without having to loop over each element. I do not want a string, as returned by $('#formid').serialize();, nor do I want the map returned by $('#formid').serializeArray();


Source: (StackOverflow)

Get current URL in JavaScript?

I am using jQuery. How do I get the path of the current URL and assign it to a variable?

Example URL:

http://localhost/menuname.de?foo=bar&amp;number=0

Source: (StackOverflow)

jQuery scroll to element

I have this input element:

<input type="text" class="textfield" value="" id="subject" name="subject">

Then I have some other elements, like other text inputs, textareas, etc.

When the user clicks on that input with #subject, the page should scroll to the last element of the page with a nice animation. It should be a scroll to bottom and not to top.

The last item of the page is a submit button with #submit:

<input type="submit" class="submit" id="submit" name="submit" value="Ok, Done.">

The animation should not be too fast and should be fluid.

I am running the latest jQuery version. I prefer to not install any plugin but to use the default jQuery features to achieve this.


Source: (StackOverflow)