I have a set of dynamically generated checkboxes, where each of them has a data-id
attribute corresponding to a database integer id. When i populate my html-form with an object to edit, there is a list of integers representing which checkboxes should be checked. The checkboxes are wrapped in a div
with class checkbox-wrapper
.
So html looks like this:
<div class="checkbox-wrapper">
<input type="checkbox" id="checkbox1" data-id="1">
<label for="checkbox1">Checkbox 1</label>
</div>
<div class="checkbox-wrapper">
<input type="checkbox" id="checkbox2" data-id="2">
<label for="checkbox2">Checkbox 2</label>
</div>
<div class="checkbox-wrapper">
<input type="checkbox" id="checkbox3" data-id="99">
<label for="checkbox3">Checkbox 99</label>
</div>
Note that the id runs on auto increment index numbers, while data-id might have a different id value. I want to select them by data-id.
Now, using JQuery, I know I can select the relevant checkboxes like this:
$(".checkbox-wrapper>input[data-id='99']");
$(".checkbox-wrapper>input[data-id='1']");
This works in my console, in chrome, and it returns the relevant DOM-element. Likewise, this below, sets the checkboxes to checked:
$(".checkbox-wrapper>input[data-id='99']").prop("checked", "checked");
$(".checkbox-wrapper>input[data-id='1']").prop("checked", "checked");
However, if I iterate through a list of integers in my javascript code (not directly in the console), and log the returned elements, based on the id values, I get some weird results:
var ids = [1,2]
$.each(ids, function(index, myID){
console.log($(".checkbox-wrapper>input[data-id='"+myID+"']"));
$(".checkbox-wrapper>input[data-id='"+myID+"']").prop("checked", "checked");
});
First of all, no checkboxes are checked. Second, my console prints strange results:
n.fn.init[0]
context: document
length: 0
prevObject: n.fn.init[1]
selector: ".checkbox-wrapper>input[data-id='1']"
__proto__: n[0]
n.fn.init[0]
context: document
length: 0
prevObject: n.fn.init[1]
selector: ".checkbox-wrapper>input[data-id='2']"
__proto__: n[0]
The printed selector Strings seems perfect. The exact same selectors returns the DOM-elements, when written directly into the chrome console. Then they return objects like this:
[<input type="checkbox" id="checkbox1" data-id="1">]
What is the n.fn.init[0], and why it is returned? Why are my two seemingly identical JQuery functions returning different things?
fn. init() {...} , is given the jQuery prototype so that its object 'type' is of jQuery , and that all instances of it are actually instances of jQuery . Follow this answer to receive notifications.
The jQuery Object: The Wrapped Set: Selectors return a jQuery object known as the "wrapped set," which is an array-like structure that contains all the selected DOM elements. You can iterate over the wrapped set like an array or access individual elements via the indexer ($(sel)[0] for example).
jQuery returns prevObject if the DOM does not have the element for which jQuery is being run. You might see the element in your source at the run-time however, it is not not bound to the DOM and therefore, it shows prevObject.
version added: 1.0jQuery( "element" ) Refers to the tagName of DOM nodes.
Another approach(Inside of $function
to asure that the each
is executed on document ready
):
var ids = [1,2];
$(function(){
$('.checkbox-wrapper>input[type="checkbox"]').each(function(i,item){
if(ids.indexOf($(item).data('id')) > -1){
$(item).prop("checked", "checked");
}
});
});
What is the n.fn.init[0], and why it is returned? Why are my two seemingly identical JQuery functions returning different things?
Answer: It seems that your elements are not in the DOM yet, when you are trying to find them. As @Rory McCrossan pointed out, the
length:0
means that it doesn't find any element based on your search criteria.
n.fn.init[0]
, lets look at the core of the Jquery Library:var jQuery = function( selector, context ) {
return new jQuery.fn.init( selector, context );
};
Looks familiar, right?, now in a minified version of jquery, this should looks like:
var n = function( selector, context ) {
return new n.fn.init( selector, context );
};
So when you use a selector you are creating an instance of the jquery function; when found an element based on the selector criteria it returns the matched elements; when the criteria does not match anything it returns the prototype object of the function.
Here is how to do a quick check to see if n.fn.init[0]
is caused by your DOM-elements not loading in time. Delay your selector function by wrapping it in setTimeout
function like this:
function timeout(){
...your selector function that returns n.fn.init[0] goes here...
}
setTimeout(timeout, 5000)
This will cause your selector function to execute with a 5 second delay, which should be enough for pretty much anything to load.
This is just a coarse hack to check if DOM is ready for your selector function or not. This is not a (permanent) solution.
The preferred ways to check if the DOM is loaded before executing your function are as follows:
1) Wrap your selector function in
$(document).ready(function(){ ... your selector function... };
2) If that doesn't work, use DOMContentLoaded
3) Try window.onload, which waits for all the images to load first, so its least preferred
window.onload = function () { ... your selector function... }
4) If you are waiting for a library to load that loads in several steps or has some sort of delay of its own, then you might need some complicated custom solution. This is what happened to me with "MathJax" library. This question discusses how to check when MathJax library loaded its DOM elements, if it is of any help.
5) Finally, you can stick with hard-coded setTimeout
function, making it maybe 1-3 seconds. This is actually the very least preferred method in my opinion.
This list of fixes is probably far from perfect so everyone is welcome to edit it.
Your result object is a jQuery element, not a javascript array. The array you wish must be under .get()
As the return value is a jQuery object, which contains an array, it's very common to call .get() on the result to work with a basic array. http://api.jquery.com/map/
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With