javascript remove previous filter on an object before applying new one - javascript

I have a series of buttons that apply filters to an object using a function similar to this:
isNew(type) {
//need to reset filter first
this.results = this.results.filter(function(type) {
return type.has_user_viewed === true
The problem I have is if one filter is applied by the user clicking, and then another filter applied, the filtered array is filtered again. What I need to do with the above is reset the object to it's original state before applying a new filter. Not sure how to "reset" a filter here?

Just save the unfiltered data to a variable. filter creates a new array object (shallow copying elements) each time, so your code overwrites the original data with the filtered data: = [...whatever the source is]
isNew(type) {
//need to reset filter first
this.results = {
return type.has_user_viewed === true

You'll probably need to store the result of the filter somewhere other than this.results if you want to access the original list of results for additional filtering later. Note that this change will likely force you to change other code.
An example of what I'm recommending:
this.filteredResults = this.results.filter(function(type) {
return type.has_user_viewed === true
I would suggest that you google immutability, as understanding it will help you greatly when you need to solve similar problems in the future.


"You may have an infinite update loop in a component render function" when I add this line of code - console.log(perksTree.slots.unshift())

I have a function that find an object from a JSON that has an id === this.match.mainParticipant.stats.perkSubStyle. This object contains a property called slots that is an array and has 4 elements. Each slot has 3 elements which represent runes from a game. If you iterate over the slots and their elements you get this:
I get the object using this function:
let perksTree = this.$store.state.summonerRunes.find(value => === this.match.mainParticipant.stats.perkSubStyle);
return perksTree
and I iterate and display the icons using this:
<div v-for='runes in this.secondaryPerks().slots'>
<div v-for='rune in runes.runes'>
<img :src="'' + rune.icon" alt="">
Now the problem is that because that perks tree is secondary one, the perks in slot[0] can never be picked because if they were picked, they'd have to be part of the primaryPerks tree. This means there's no point displaying that none of them were selected. For that reason I am trying to remove the first slot[0] element from the array, however, when I try to unshift() it, I get an error:
"You may have an infinite update loop in a component render function"
And I have no clue why. Any advices?
Firstly, I think you mean shift rather than unshift. unshift will try to add items to the array rather than removing them. It doesn't actually matter from the perspective of the infinite loop, either method will have the same effect.
You're creating a dependency on the array and then modifying it. Modifying it will trigger a re-render.
Each time the component re-renders it will shift another item onto/out of the array. Even if the call to shift/unshift doesn't actually change anything it will still count as modifying the array.
computed: {
secondaryPerkSlots () {
const perksTree = this.$store.state.summonerRunes.find(
value => === this.match.mainParticipant.stats.perkSubStyle
return perksTree.slots.slice(1)
<div v-for='runes in secondaryPerkSlots'>
That will create a new array containing the same elements as the original array, omitting the first element.
Alternatively you could put the slice(1) directly in the template:
<div v-for='runes in secondaryPerks().slots.slice(1)'>
Either way I suggest changing the method to a computed property instead. You should also drop the this in your template.
I had the same problem a few months ago.
I think the main issue is that you perform logic such as arr.unshift()(which will cause the template to re-render in this case) in your computed property.
So, imagine this:
const arr1 = [/* ... */];
// This is different
const computedArr = () => {
return arr.filter(() => { /* ... */ });
// Than this
const computedArr = () => {
const newArr = arr.filter(() => { /* ... */ });
// Vue cannot allow this without a re-render!
return newArr;
The latter will cause the template to re-render;
Check the first comment!

Trying to dynamically organize JSON object elements into different arrays based on values

This is the JSON I'm working with:$where=camis%20=%2230112340%22
I'd be dynamically making the queries using different data, so it'll possibly change.
What I'm essentially trying to do is to somehow organize the elements within this array into different arrays based on inspection_date.
So for each unique inspection_date value, those respective inspections would be put into its own collection.
If I knew the dates beforehand, I could easily iterate through each element and just push into an array.
Is there a way to dynamically create the arrays?
My end goal is to be able to display each group of inspections (based on inspection date) using Angular 5 on a webpage. I already have the site up and working and all of the requests being made.
So, I'm trying to eventually get to something like this. But of course, using whatever dates in the response from the request.
List the inspections
List the inspections
List the inspections
Just for reference, here's the code I'm using:
ngOnInit() {
this.route.params.subscribe(params => {
this.title = +params['camis']; // (+) converts string 'id' to a number
this.q.getInpectionsPerCamis(this.title).subscribe((res) => {
this.inspectionList = res;
// In a real app: dispatch action to load the details here.
I wish I could give you more info, but at this point, I'm just trying to get started.
I wrote this in jQuery just because it was faster for me, but it should translate fairly well to Angular (I just don't want to fiddle with an angular app right now)
Let me know if you have any questions.
$(function() {
let byDateObj = {};
url: '$where=camis%20=%2230112340%22'
}).then(function(data) {
//probably do a check to make sure the data is an array, im gonna skip that
byDateObj = data.reduce(function(cum, cur) {
if (!cum.hasOwnProperty(cur.inspection_date)) cum[cur.inspection_date] = [];
//if the cumulative array doesn't have the inspection property already, add it as an empty array
//push to inspection_date array.
return cum;
//return cumulatie object
}, byDateObj);
//start with an empty object by default;
}, console.error);
<script src=""></script>

Filter through Angular Collection fast

I know it's trivial but I have a doubt to be clarified.
I have a collection vm.groups that has almost 1000 objects. Now, each object has name, id, links etc. property fields.
Grid only displays name and id.
Now, there is a text box where we enter some text and we have to filter data, according to whatever we entered but filtering must happen only within name and id fields of the objects not the other fields that are present within the objects.
So, both things can be done,
1) I create a temp collection from the original collection objects with only name and id fields and then bind the collection to view.
// vm.groups.forEach(function(element) {
// vm.displayedFieldGroups.
// push({name:,id:,transformedId: element.transformedId});
// });
2) Or, I create a custom filter vm.customSearch :
vm.customSearch = function(searchVal) {
if(vm.filter.length) {
if(vm.filter.toLowerCase().indexOf( !== -1 ||
vm.filter.toLowerCase().indexOf( !== -1) {
return true;
}else {
return false;
} else {
return true;
And in the view vm.groups | filter: vm.customSearch.
But I think second method is slower because each value in the collection would be passed to the filter which is obviously tedious for huge collection.
Am I right?
Which is the right way to do?
This was for a legacy application. There was a filter already implemented but that just goes through all the fields in the object. I need to only filter for name and id fields of objects.
Hence, I need to either create a custom filter or choose the first approach that I depicted.
You're right in your assumption that the filter would go over every item in the source array and run your filter function each time there's a digest cycle.
You should proceed with the first approach.

ES6 class getter, temporary return or alternative solution

I am trying to solve a problem I am seeing when rendering a list of items in my ui that is coming out of a es6 class I have created. The model is working great, however I am using animations that are listening to (in react) mount, onEnter, and onLeave of the items.
When I apply my filters and sorting via the model and spit back the new list of items via the getter, the animations do not apply to some items because the list is just being re sorted, not necessarily changed.
So my getter just grabs this.products of the class and returns it and applies a sort order to it. And if filters are applied (which are tracked by this._checkedList in the class), the this.products is reduced based on which filters are selected then sorted. So that getter looks like so :
get productList() {
if (this._checkedList.length > 0) {
const filteredProducts = _.reduce(this.filterMap, reduceFilters, []);
const deDuped = _.uniq(filteredProducts, 'id');
return this.applySort(deDuped);
const deDuped = _.uniq(this.products, 'id');
return this.applySort(deDuped);
What I am trying to figure out, is a way to to temporarily send back an empty array while the filters or sorting run. The reason being the ui would receive an empty array (even if for a split second) and react would register the new sorted/filtered list as a new list and fire the enter/leave/mount animations again.
My attempt was to set a local property of the class like -
this._tempReturn = false;
then in the functions where the sort or filter happen, I set it to true, then back to false when the function is done like this -
toggleFilter(args) {
this._tempReturn = true;
...toggle logic
this._tempReturn = false;
Then changed the getter to check for that property before i do anything else, and if it's true, send back an empty array -
get productList() {
if (this._tempReturn) {
return [];
However, this does not seem to work. Even putting a console.log in the if (this._tempReturn) { didn't show any logs.
I also tried sending back a new list with lodash's _.cloneDeep like so :
get productList() {
if (this._checkedList.length > 0) {
const filteredProducts = _.reduce(this.filterMap, reduceFilters, []);
const deDuped = _.uniq(filteredProducts, 'id');
return _.cloneDeep(this.applySort(deDuped));
const deDuped = _.uniq(this.products, 'id');
return _.cloneDeep(this.applySort(deDuped));
this did not work either. So it seems the empty array return might be a better approach.
I am wondering if there is some way to achieve this - I would like to have the array be return empty for a second perhaps while the filters and sort are applying.
Very stuck on how to achieve, perhaps I am even looking at this problem from the wrong angle and there is a much better way to solve this. Any advice would be welcomed, thanks for reading!
In order to force a re-render of items in a list when updating them you just need to make sure that each items has a unique key property.
Instead of rendering the list, then rendering it as empty, then re-rendering a changed list make sure each child has a unique key. Changing the key property on a child in an array will always cause it to re-render.

Display posts in descending posted order

I'm trying to test out Firebase to allow users to post comments using push. I want to display the data I retrieve with the following;
fbl.child('sell').limit(20).on("value", function(fbdata) {
// handle data display here
The problem is the data is returned in order of oldest to newest - I want it in reversed order. Can Firebase do this?
Since this answer was written, Firebase has added a feature that allows ordering by any child or by value. So there are now four ways to order data: by key, by value, by priority, or by the value of any named child. See this blog post that introduces the new ordering capabilities.
The basic approaches remain the same though:
1. Add a child property with the inverted timestamp and then order on that.
2. Read the children in ascending order and then invert them on the client.
Firebase supports retrieving child nodes of a collection in two ways:
by name
by priority
What you're getting now is by name, which happens to be chronological. That's no coincidence btw: when you push an item into a collection, the name is generated to ensure the children are ordered in this way. To quote the Firebase documentation for push:
The unique name generated by push() is prefixed with a client-generated timestamp so that the resulting list will be chronologically-sorted.
The Firebase guide on ordered data has this to say on the topic:
How Data is Ordered
By default, children at a Firebase node are sorted lexicographically by name. Using push() can generate child names that naturally sort chronologically, but many applications require their data to be sorted in other ways. Firebase lets developers specify the ordering of items in a list by specifying a custom priority for each item.
The simplest way to get the behavior you want is to also specify an always-decreasing priority when you add the item:
var ref = new Firebase('');
var item = ref.push();
item.setWithPriority(yourObject, 0 -;
You'll also have to retrieve the children differently:
fbl.child('sell').startAt().limitToLast(20).on('child_added', function(fbdata) {
In my test using on('child_added' ensures that the last few children added are returned in reverse chronological order. Using on('value' on the other hand, returns them in the order of their name.
Be sure to read the section "Reading ordered data", which explains the usage of the child_* events to retrieve (ordered) children.
A bin to demonstrate this:,console
Since firebase 2.0.x you can use limitLast() to achieve that:
fbl.child('sell').orderByValue().limitLast(20).on("value", function(fbdataSnapshot) {
// fbdataSnapshot is returned in the ascending order
// you will still need to order these 20 items in
// in a descending order
Here's a link to the announcement: More querying capabilities in Firebase
To augment Frank's answer, it's also possible to grab the most recent records--even if you haven't bothered to order them using priorities--by simply using endAt().limit(x) like this demo:
var fb = new Firebase(URL);
// listen for all changes and update
fb.endAt().limit(100).on('value', update);
// print the output of our array
function update(snap) {
var list = [];
snap.forEach(function(ss) {
var data = ss.val();
data['.priority'] = ss.getPriority();
data['.name'] =;
// print/process the results...
Note that this is quite performant even up to perhaps a thousand records (assuming the payloads are small). For more robust usages, Frank's answer is authoritative and much more scalable.
This brute force can also be optimized to work with bigger data or more records by doing things like monitoring child_added/child_removed/child_moved events in lieu of value, and using a debounce to apply DOM updates in bulk instead of individually.
DOM updates, naturally, are a stinker regardless of the approach, once you get into the hundreds of elements, so the debounce approach (or a React.js solution, which is essentially an uber debounce) is a great tool to have.
There is really no way but seems we have the recyclerview we can have this
// Initialize Views
mRecyclerView = (RecyclerView) view.findViewById(;
mManager = new LinearLayoutManager(getContext());
// mManager.setReverseLayout(false);
I have a date variable (long) and wanted to keep the newest items on top of the list. So what I did was:
Add a new long field 'dateInverse'
Add a new method called 'getDateInverse', which just returns: Long.MAX_VALUE - date;
Create my query with: .orderByChild("dateInverse")
Presto! :p
You are searching limitTolast(Int x) .This will give you the last "x" higher elements of your database (they are in ascending order) but they are the "x" higher elements
if you got in your database {10,300,150,240,2,24,220}
this method:
will retrive you : {150,220,240,300}
In Android there is a way to actually reverse the data in an Arraylist of objects through the Adapter. In my case I could not use the LayoutManager to reverse the results in descending order since I was using a horizontal Recyclerview to display the data. Setting the following parameters to the recyclerview messed up my UI experience:
The only working way I found around this was through the BindViewHolder method of the RecyclerView adapter:
public void onBindViewHolder(final RecyclerView.ViewHolder holder, int position) {
final SuperPost superPost = superList.get(getItemCount() - position - 1);
Hope this answer will help all the devs out there who are struggling with this issue in Firebase.
Firebase: How to display a thread of items in reverse order with a limit for each request and an indicator for a "load more" button.
This will get the last 10 items of the list
.limitToLast(loadMoreLimit) // loadMoreLimit = 10 for example
This will get the last 10 items. Grab the id of the last record in the list and save for the load more functionality. Next, convert the collection of objects into and an array and do a list.reverse().
LOAD MORE Functionality: The next call will do two things, it will get the next sequence of list items based on the reference id from the first request and give you an indicator if you need to display the "load more" button.
.endAt(null, lastThreadId) // Get this from the previous step
You will need to strip the first and last item of this object collection. The first item is the reference to get this list. The last item is an indicator for the show more button.
I have a bunch of other logic that will keep everything clean. You will need to add this code only for the load more functionality.
list = snapObjectAsArray; // The list is an array from snapObject
lastItemId = key; // get the first key of the list
if (list.length < loadMoreLimit+1) {
lastItemId = false;
if (list.length > loadMoreLimit+1) {
if (list.length > loadMoreLimit) {
// Return the list.reverse() and lastItemId
// If lastItemId is an ID, it will be used for the next reference and a flag to show the "load more" button.
I'm using ReactFire for easy Firebase integration.
Basically, it helps me storing the datas into the component state, as an array. Then, all I have to use is the reverse() function (read more)
Here is how I achieve this :
import React, { Component, PropTypes } from 'react';
import ReactMixin from 'react-mixin';
import ReactFireMixin from 'reactfire';
import Firebase from '../../../utils/firebaseUtils'; // Firebase.initializeApp(config);
export default class Add extends Component {
constructor(args) {
this.state = {
articles: []
componentWillMount() {
let ref = Firebase.database().ref('articles').orderByChild('insertDate').limitToLast(10);
this.bindAsArray(ref, 'articles'); // bind retrieved data to this.state.articles
render() {
return (
this.state.articles.reverse().map(function(article) {
return <div>{article.title}</div>
There is a better way. You should order by negative server timestamp. How to get negative server timestamp even offline? There is an hidden field which helps. Related snippet from documentation:
var offsetRef = new Firebase("https://<YOUR-FIREBASE-APP>");
offsetRef.on("value", function(snap) {
var offset = snap.val();
var estimatedServerTimeMs = new Date().getTime() + offset;
To add to Dave Vávra's answer, I use a negative timestamp as my sort_key like so
const timestamp = new Date().getTime();
const data = {
name: 'John Doe',
city: 'New York',
sort_key: timestamp * -1 // Gets the negative value of the timestamp
const ref = firebase.database().ref('business-images').child(id);
const query = ref.orderByChild('sort_key');
return $firebaseArray(query); // AngularFire function
This fetches all objects from newest to oldest. You can also $indexOn the sortKey to make it run even faster
I had this problem too, I found a very simple solution to this that doesn't involved manipulating the data in anyway. If you are rending the result to the DOM, in a list of some sort. You can use flexbox and setup a class to reverse the elements in their container.
.reverse {
display: flex;
flex-direction: column-reverse;
myarray.reverse(); or this.myitems = => item).reverse();
I did this by prepend.
query.orderByChild('sell').limitToLast(4).on("value", function(snapshot){
snapshot.forEach(function (childSnapshot) {
Someone has pointed out that there are 2 ways to do this:
Manipulate the data client-side
Make a query that will order the data
The easiest way that I have found to do this is to use option 1, but through a LinkedList. I just append each of the objects to the front of the stack. It is flexible enough to still allow the list to be used in a ListView or RecyclerView. This way even though they come in order oldest to newest, you can still view, or retrieve, newest to oldest.
You can add a column named orderColumn where you save time as
Long refrenceTime = "large future time";
Long currentTime = "currentTime";
Long order = refrenceTime - currentTime;
now save Long order in column named orderColumn and when you retrieve data
as orderBy(orderColumn) you will get what you need.
just use reverse() on the array , suppose if you are storing the values to an array items[] then do a this.items.reverse()
ref.subscribe(snapshots => {
this.items = [];
snapshots.forEach(snapshot => {
For me it was limitToLast that worked. I also found out that limitLast is NOT a function:)
const query = messagesRef.orderBy('createdAt', 'asc').limitToLast(25);
The above is what worked for me.
PRINT in reverse order
Let's think outside the box... If your information will be printed directly into user's screen (without any content that needs to be modified in a consecutive order, like a sum or something), simply print from bottom to top.
So, instead of inserting each new block of content to the end of the print space (A += B), add that block to the beginning (A = B+A).
If you'll include the elements as a consecutive ordered list, the DOM can put the numbers for you if you insert each element as a List Item (<li>) inside an Ordered Lists (<ol>).
This way you save space from your database, avoiding unnecesary reversed data.