I have a jQuery object array that I need to remove the 1st and last item from. I tried using shift() and pop() but it threw an error because I guess a jQuery object is not the same as an array? I then used delete however that doesn't change the length so a loop I have after this gets all kinds of messed up. Finally I found out I should use:
$item.splice(0,1) and $item.splice($item.length-1, 1)
however the object array that splice(0, 1) returns is no longer in the same order as it was previously. Is there a reason splice would return a different order?
Did you try using slice? It works with a jQuery elements collection:
$('div').slice(1, -1);
Also, you can use the above statement without changing your original array. It returns the collection, removing the first and last elements.
Related
i've been googling around about how to add an object into an array in firestore, and found the arrayUnion() able to add an object into firestore array, but it only add the object into last index of array, but how to add it into first index of array?
//add "greater_virginia" into last index of array
washingtonRef.update({
regions: firebase.firestore.FieldValue.arrayUnion("greater_virginia")
});
//how to add "greater_virginia" into first index of array?
its basically same as arrayUnion but instead of add it into last index, i want to add it into first index of array.
If Firestore arrays behave anything like realtime-database arrays, then they don't actually exist. As far as I know, they are store as maps, like:
{
0: "first element",
2: "second and so on",
}
You can probably see how an unshift would be a big transformation. In fact, firestore doesn't let you do this, saying "...in order to avoid some of the issues that can arise in a multi-user environment, you'll be adding them with more of a set-like functionality".
With that in mind, this problem is usually solved at the application level by fetching the array, mutating it as needed, then setting the whole thing.
Bit of further reading https://firebase.googleblog.com/2018/08/better-arrays-in-cloud-firestore.html
PS: be careful with the arrayUnion operator, because it actually performs a add to set
Firestore doesn't offer any way to modify items of array fields by index. arrayUnion will only ever append to the end of the array if the element doesn't already exist.
If you want to modify an array by index, you will have to read the document, modify the array in memory to appear how you want, then write the modified array back to the document.
I am using linqjs and I have one array full of ids to include in a list, and an array full of complex objects which have a property userId.
Problem is when I do an intersection it never seems to return anything, however there is very little information around the compareSelector.
So here is an example of what I am doing:
enumerableOfUsers.intersect(listOfIdsToInclude, "$.userId");
So in the above example enumerableOfUsers would be an existing enumerable created from an array of users (which contain the userId field), the listOfIdsToInclude is an array of id values, like ["12345", "213213", "2124"] etc.
The intersect seems to work but never returns anything and I know the userIds match so am I doing anything wrong here?
The thing is that the compare selector is applied to items of both the first and second sets. The second set is a list of ids already so the compare selector doesn't apply. The projection yields undefined values which will always result in no results found.
You need to apply the selector only to the first set of values. Try this instead:
// using linqjs 2.x syntax
var query = enumerableOfUsers.Select("$.userId").Intersect(listOfIdsToInclude);
So...I have this array:
val['an_element'][0]['another_element'][2]['text']
I want to get rid of the entire "2" node.
Now...I THOUGHT the way to do this would be:
delete val['an_element'][0]['another_element'][2];
BUT...it doesn't actually drop the element, but simply empties it out.
I also tried:
val['an_element'][0]['another_element'][2] = null;
...but that just resulted in my console log nearly bleeding it was so red with errors.
Basically, i want that [2] node to NO LONGER EXIST. Basically, I want it to NOT BE FOUND AT ALL.
What do I do??? And I know the ".splice" method will NOT actually modify the original array, so please don't suggest it. :)
The splice method will, in fact, modify the array. Just try:
val['an_element'][0]['another_element'].splice(2, 1);
From the docs:
Changes the content of an array, adding new elements while removing old elements.
...
If you specify a different number of elements to insert than the number you're removing, the array will have a different length at the end of the call.
I'm wondering, why do some elements appear like an array and others like HTMLSpanElement. I've attached a picture as I'm not sure how to describe this otherwise.
The following log is made via
log(returner);
log(returner[0]);
Is returner a jQuery object as a result of $() ? $() will always return an array, even if there is one or zero elements inside of it. Without specifying an index in your first console.log, the entire contents of the array are outputted. In the second console.log, you include an array index, so only the element matching that index is outputted.
Because the element that appears like an array IS an array - it's an array of DOM element objects (HTMLSpanElement, etc).
When you log the first element of the array with returner[0], that element is a DOM object, so it logs it as an object.
Because (it looks like) returner is not an element, but an array of elements.
I have an array called as wcs declared using var wcs= new Array();.
I do add items like this, wcs[indx] = value. where i will keep on changing the indx value, so at times, my array will be looking like this
wcs[2] ='a'; wcs[5]=')';
when i call the splice method on this array, all the created indices are re-indexed, meaning they become reset from 0...
how to avoid this in javascript & jQuery
Write your own splice method that works the way you want. If you specify the input, processing and expected output, you might get some help with that.
If you simply want a copy of the array, you may be after the concat method.