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AngularJS ng-repeat is slow

It is not like it is slow on rendering many entries. The problem is that whenever the $scope.data got updated, it adds the new item first at the end of the element, then reduce it as it match the new $scope.data.
For example:
<div class="list" ng-repeat="entry in data">
<h3>{{entry.title}}</h3>
</div>
This script is updating the $scope.data:
$scope.load = function() {
$scope.data = getDataFromDB();
}
Lets say I have 5 entries inside $scope.data. The entries are:
[
{
id: 1,
title: 1
},
{
id: 2,
title: 2
},
......
]
When the $scope.data already has those entries then got reloaded ($scope.data = getDataFromDB(); being called), the DOM element for about 0.1s - 0.2s has 10 elements (duplicate elements), then after 0.1s - 0.2s it is reduced to 5.
So the problem is that there is delay about 0.1s - 0.2s when updating the ng-repeat DOM. This looks really bad when I implement live search. Whenever it updates from the database, the ng-repeat DOM element got added up every time for a brief millisecond.
How can I make the rendering instant?
EDITED
I will paste all my code here:
The controller:
$scope.search = function (table) {
$scope.currentPage = 1;
$scope.endOfPage = false;
$scope.viewModels = [];
$scope.loadViewModels($scope.orderBy, table);
}
$scope.loadViewModels = function (orderBy, table, cb) {
if (!$scope.endOfPage) {
let searchKey = $scope.page.searchString;
let skip = ($scope.currentPage - 1) * $scope.itemsPerPage;
let searchClause = '';
if (searchKey && searchKey.length > 0) {
let searchArr = [];
$($scope.vmKeys).each((i, key) => {
searchArr.push(key + ` LIKE '%` + searchKey + `%'`);
});
searchClause = `WHERE ` + searchArr.join(' OR ');
}
let sc = `SELECT * FROM ` + table + ` ` + searchClause + ` ` + orderBy +
` LIMIT ` + skip + `, ` + $scope.itemsPerPage;
sqlite.query(sc, rows => {
$scope.$apply(function () {
var data = [];
let loadedCount = 0;
if (rows != null) {
$scope.currentPage += 1;
loadedCount = rows.length;
if (rows.length < $scope.itemsPerPage)
$scope.endOfPage = true
for (var i = 0; i < rows.length; i++) {
let item = rows.item(i);
let returnObject = {};
$($scope.vmKeys).each((i, key) => {
returnObject[key] = item[key];
});
data.push(returnObject);
}
$scope.viewModels = $scope.viewModels.concat(data);
}
else
$scope.endOfPage = true;
if (cb)
cb(loadedCount);
})
});
}
}
The view:
<div id="pageContent" class="root-page" ng-controller="noteController" ng-cloak>
<div class="row note-list" ng-if="showList">
<h3>Notes</h3>
<input ng-model="page.searchString" id="search"
ng-keyup="search('notes')" type="text" class="form-control"
placeholder="Search Notes" style="margin-bottom:10px">
<div class="col-12 note-list-item"
ng-repeat="data in viewModels track by data.id"
ng-click="edit(data.id)"
ontouchstart="touchStart()" ontouchend="touchEnd()"
ontouchmove="touchMove()">
<p ng-class="deleteMode ? 'note-list-title w-80' : 'note-list-title'"
ng-bind-html="data.title"></p>
<p ng-class="deleteMode ? 'note-list-date w-80' : 'note-list-date'">{{data.dateCreated | displayDate}}</p>
<div ng-if="deleteMode" class="note-list-delete ease-in" ng-click="delete($event, data.id)">
<span class="btn fa fa-trash"></span>
</div>
</div>
<div ng-if="!deleteMode" ng-click="new()" class="add-btn btn btn-primary ease-in">
<span class="fa fa-plus"></span>
</div>
</div>
<div ng-if="!showList" class="ease-in">
<div>
<div ng-click="back()" class="btn btn-primary"><span class="fa fa-arrow-left"></span></div>
<div ng-disabled="!isDataChanged" ng-click="save()" class="btn btn-primary" style="float:right">
<span class="fa fa-check"></span>
</div>
</div>
<div contenteditable="true" class="note-title"
ng-bind-html="selected.title" id="title">
</div>
<div contenteditable="true" class="note-container" ng-bind-html="selected.note" id="note"></div>
</div>
</div>
<script src="../js/pages/note.js"></script>
Calling it from:
$scope.loadViewModels($scope.orderBy, 'notes');
The sqlite query:
query: function (query, cb) {
db.transaction(function (tx) {
tx.executeSql(query, [], function (tx, res) {
return cb(res.rows, null);
});
}, function (error) {
return cb(null, error.message);
}, function () {
//console.log('query ok');
});
},
It is apache cordova framework, so it uses webview in Android emulator.
My Code Structure
<html ng-app="app" ng-controller="pageController">
<head>....</head>
<body>
....
<div id="pageContent" class="root-page" ng-controller="noteController" ng-cloak>
....
</div>
</body>
</html>
So there is controller inside controller. The parent is pageController and the child is noteController. Is a structure like this slowing the ng-repeat directives?
Btw using track by is not helping. There is still delay when rendering it. Also I can modify the entries as well, so when an entry was updated, it should be updated in the list as well.
NOTE
After thorough investigation there is something weird. Usually ng-repeat item has hash key in it. In my case ng-repeat items do not have it. Is it the cause of the problem?

One approach to improve performance is to use the track by clause in the ng-repeat expression:
<div class="list" ng-repeat="entry in data track by entry.id">
<h3>{{entry.title}}</h3>
</div>
From the Docs:
Best Practice: If you are working with objects that have a unique identifier property, you should track by this identifier instead of the object instance, e.g. item in items track by item.id. Should you reload your data later, ngRepeat will not have to rebuild the DOM elements for items it has already rendered, even if the JavaScript objects in the collection have been substituted for new ones. For large collections, this significantly improves rendering performance.
For more information, see
AngularJS ngRepeat API Reference -- Tracking and Duplicates

In your html, try this:
<div class="list" ng-repeat="entry in data">
<h3 ng-bind="entry.title"></h3>
</div>

After thorough research, I found my problem. Every time I reset / reload my $scope.viewModels I always assign it to null / empty array first. This what causes the render delay.
Example:
$scope.search = function (table) {
$scope.currentPage = 1;
$scope.endOfPage = false;
$scope.viewModels = []; <------ THIS
$scope.loadViewModels($scope.orderBy, table);
}
So instead of assigning it to null / empty array, I just replace it with the new loaded data, and the flickering is gone.

How to efficiently build a document fragment [duplicate]

I'm currently using AJAX with Django Framework.
I can pass asynchronous POST/GET to Django, and let it return a json object.
Then according to the result passed from Django, I will loop through the data, and update a table on the webpage.
The HTML for the table:
<!-- Modal for Variable Search-->
<div class="modal fade" id="variableSearch" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
<div class="modal-dialog">
<div class="modal-content">
<div class="modal-header">
<button type="button" class="close" data-dismiss="modal"><span aria-hidden="true">×</span><span class="sr-only">Close</span></button>
<h4 class="modal-title" id="myModalLabel">Variable Name Search</h4>
</div>
<div class="modal-body">
<table id="variableSearchTable" class="display" cellspacing="0" width="100%">
<thead>
<tr>
<th> Variable Name </th>
</tr>
</thead>
</table>
<p>
<div class="progress">
<div class="progress-bar progress-bar-striped active" id="variableSearchProgressBar" role="progressbar" aria-valuenow="45" aria-valuemin="0" aria-valuemax="100" style="width: 45%">
<span class="sr-only">0% Complete</span>
</div>
</div>
</p>
<p>
<div class="row">
<div class="col-lg-10">
<button class="btn btn-default" type="button" id="addSearchVariable" >Add</button>
</div>
</div>
</p>
</div>
<div class="modal-footer">
<button type="button" class="btn btn-default" id="variableSearchDataCloseButton" data-dismiss="modal">Close</button>
</div>
</div>
</div>
</div>
Basically it is a bootstrap 3 modal, with jQuery DataTable, and with a progress bar to show the user the current progress.
The Javascript that is used to get Django results:
$('#chartSearchVariable').click(function(event)
{
$('#chartConfigModal').modal("hide");
$('#variableSearch').modal("show");
var csrftoken = getCookie('csrftoken');
var blockname = document.getElementById('chartConfigModalBlockname').value;
$('#variableSearchProgressBar').css('width', "0%").attr('aria-valuenow', "0%");
event.preventDefault();
$.ajax(
{
type:"GET",
url:"ajax_retreiveVariableNames/",
timeout: 4000000,
data:
{
'csrfmiddlewaretoken':csrftoken,
'blockname':blockname
},
success: function(response)
{
if(response.status == "invalid")
{
$('#chartConfigModal').modal("hide");
$('#variableSearch').modal("hide");
$('#invalid').modal("show");
}
else
{
configurationVariableChart.row('').remove().draw(false);
for (i = 0 ; i < response.variables.length; i++)
{
configurationVariableChart.row.add(
$(
'<tr>' +
'<td>' + response.variables[i] + '</td>' +
'<tr>'
)[0]);
}
configurationVariableChart.draw();
$('#variableSearchProgressBar').css('width', "100%").attr('aria-valuenow', "100%");
}
},
failure: function(response)
{
$('#chartConfigModal').modal("hide");
$('#variableSearch').modal("hide");
$('#invalid').modal("show");
}
});
return false;
});
$('#addSearchVariable').click(function(event)
{
$('#variableSearch').modal("hide");
$('#chartConfigModal').modal("show");
document.getElementById('chartConfigModalVariable').value = currentVariableNameSelects;
});
$('#variableSearchDataCloseButton').click(function(event)
{
$('#variableSearch').modal("hide");
$('#chartConfigModal').modal("show");
});
The problem is with the updating table part:
configurationVariableChart.row('').remove().draw(false);
for (i = 0 ; i < response.variables.length; i++)
{
configurationVariableChart.row.add(
$(
'<tr>' +
'<td>' + response.variables[i] + '</td>' +
'<tr>'
)[0]);
}
configurationVariableChart.draw();
$('#variableSearchProgressBar').css('width', "100%").attr('aria-valuenow', "100%");
Since the response.variables can be over 10k, and it will freeze the web browser, even though it is still drawing.
I'm pretty new to Web Design (less than 4 months), but I assume it's because they are all running on the same thread.
Is there a way in Javascript to do threading/async? I had a search, and the results were deferred/promise which seems very abstract at the moment.

Try processing retrieved data incrementally.
At piece below , elements generated in blocks of 250 , primarily utilizing jQuery deferred.notify() and deferred.progress().
When all 10,000 items processed , the deferred object is resolved with the collection of 10,000 elements. The elements are then added to document at single call to .html() within deferred.then()'s .done() callback ; .fail() callback cast as null .
Alternatively , could append elements to the document in blocks of 250 , within deferred.progress callback ; instead of at the single call within deferred.done , which occurs upon completion of the entire task.
setTimeout is utilized to prevent "freeze the web browser" condition .
$(function() {
// 10k items
var arr = $.map(new Array(10000), function(v, k) {
return v === undefined ? k : null
});
var len = arr.length;
var dfd = new $.Deferred();
// collection of items processed at `for` loop in blocks of 250
var fragment = [];
var redraw = function() {
for (i = 0 ; i < 250; i++)
{
// configurationVariableChart.row.add(
// $(
fragment.push('<tr>' +
'<td>' + arr[i] + '</td>' +
'</tr>')
// )[0]);
};
arr.splice(0, 250);
console.log(fragment, arr, arr.length);
return dfd.notify([arr, fragment])
};
$.when(redraw())
// `done` callbacks
.then(function(data) {
$("#results").html(data.join(","));
delete fragment;
}
// `fail` callbacks
, null
// `progress` callbacks
, function(data) {
// log , display `progress` of tasks
console.log(data);
$("progress").val(data[1].length);
$("output:first").text(Math.floor(data[1].length / 100) + "%");
$("output:last").text(data[1].length +" of "+ len + " items processed");
$("#results").html("processing data...");
if (data[0].length) {
var s = setTimeout(function() {
redraw()
}, 100)
} else {
clearTimeout(s);
dfd.resolve(data[1]);
}
})
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<progress min="0" max="10000"></progress><output for="progress"></output>
<output for="progress"></output><br />
<table id="results"></table>
jsfiddle http://jsfiddle.net/guest271314/ess28zLh/

Deferreds/promises won't help you here. JS in the browser is always single-threaded.
The trick is not to build up DOM elements via JS. That is always going to be expensive and slow. Rather than passing data in JSON from Django and building up a DOM dynamically, you should get Django to render a template fragment on the server side and pass that whole thing to the front-end, where the JS can simply insert it at the relevant point.

Load more data using vue js when page is bottom area

I tried to make my Load More data when my page scroll to the bottom. The first thing is I make a div element that I put at the end of the data loop.
<div class="products">
<p>{{ status }}</p>
<div class="product" v-for="(item, index) in items">
<div>
<div class="product-image"><img :src="item.link" alt=""></div>
</div>
<div>
<h4 class="product-title">{{ item.title }}</h4>
<p>Price : {{ price }}</p>
<button class="add-to-cart btn" #click="addItem(index)">Add Item To Cart</button>
</div>
</div>
<div id="product-list-bottom"></div>
</div>
Div element with id product-list-bottom I will detect it using scrollMonitor.js
My default data :
data: {
status: 'Empty product',
total: 0,
items: [],
cart: [],
newSearch: 'anime',
lastSearch: '',
price: STATIC_PRICE,
result: []
}
Inside mounted I detected scroll to bottom :
mounted: function() {
this.onSubmit()
var vueInstance = this
var elem = document.getElementById('product-list-bottom')
var watcher = scrollMonitor.create(elem)
watcher.enterViewport(function() {
vueInstance.appendItems()
})
}
Inside mounted I call onSubmit :
onSubmit: function() {
this.items = ''
this.status = "Searching keyword '" + this.newSearch + "' on server ..."
this.$http.get('/search/'.concat(this.newSearch))
.then(function(response) {
this.lastSearch = this.newSearch,
this.status = 'Find ' + response.data.length + ' data'
this.result = response.data
this.appendItems()
})
}
And inside onSubmit I call appendItems function :
appendItems: function() {
if(this.items.length < this.result.length) {
var start = this.items.length
var end = parseInt(this.items.length + 5)
var append = this.result.slice(start, end)
this.items = this.items.concat(append)
console.log(append)
}
}
All goes well, but when I scroll down I get an error message :
This is because this line :
this.items = this.items.concat(append)
How do I make the data on xxx change (always added five new data from the array) according to the command on the line :
var end = parseInt(this.items.length + 5)
Thanks

it seems '/search/'.concat(this.newSearch) gets evaluated into function and not an actual string value
Try this if you are using babel/webpack
this.$http.get(`/search/`${this.newSearch}`)
Or if not
this.$http.get('/search/' + this.newSearch)

I think since Vue 2.3+ or so you can get this done without any jQuery stuff or any other dependencies:
<style>
.scrollbar{
overflow-y: scroll;
//...
}
.styled-scrollbar::-webkit-scrollbar
.styled-scrollbar::-webkit-scrollbar-thumb
.styled-scrollbar::-webkit-scrollbar-track{
//styling
}
</style>
<template>
//...
<div #scroll="scroll" class="scrollbar">
<div v-for="item in items" :key="item.id">
//TODO: item content
</div
</div>
//...
</template>
<script>
{
data: {
//..
lastScrollUpdate:0
}
//..
mounted: {
scroll:function (e) {
var scrollBar=e.target;
if((scrollBar.scrollTop + scrollBar.clientHeight >= scrollBar.scrollHeight-20)){
var t=new Date().getTime();
if((t-this.lastScrollUpdate)>3000){
this.lastScrollUpdate=t;
console.log('reached end: '+scrollBar.scrollTop+' '+scrollBar.clientHeight+' '+scrollBar.scrollHeight);
//TODO: load more data
}else{
console.log("< 3sec between scoll. no update");
}
}
},
//..
}
}
</script>
You may also want to adjust this to "#scroll.passive", in order to let the scroll-function be executed parallel to the UI (https://v2.vuejs.org/v2/guide/events.html#Event-Modifiers)

How might I avoid opening a new window in due to watch results?

Please, look into my code. I would like to avoid opening a new window in due to watching results. I would like to avoid showing results instead of current content in the same window.
I have thought about using AJAX to show results in Dialog window (JQueryUI)
https://jqueryui.com/dialog/
but I have no idea how? Thank You in advance :)
HTML: result_browser.html
<form class="form" method="post" id="resultbrowserform">
<!--Something-->
<button type="submit" class="btn btn-default"> Apply </button>
</form>
<div id="dialog" title="Details">
<p></p>
</div>
JS:
$(function () { function serializeForm(form){...}
...
$('#resultbrowserform').submit(function () {
$.ajax({
type: 'POST',
url: '/result_browser/data/',
data: serializeForm($('#resultbrowserform')),
success: function (data, status, jqXHR) {
$('#resultbrowsertablecontainer').remove();
data = data.data;
if (!data.length) {
window.alert('No data for selected time period');
return;
}
div = $('<div id="resultbrowsertablecontainer">');
table = $('<table class="table table-striped">');
header = $('<thead>');
header.append($('<tr>')
.append( $('<th>').html('Die Id'))
.append( $('<th>').html('Application'))
.append( $('<th>').html('Result'))
table.append(header);
body = $('<tbody>');
for (i = 0; i < data.length; i++) {
row = $('<tr>');
row.append( $('<td>').html(data[i].die_id));
row.append( $('<td>').html(data[i].application));
row.append( $('<td>').html(data[i].result));
<!--I would like to avoid opening a new window-->
link = $('<a>').attr('target', '_blank').attr('href', '/result_details/' + data[i].result_id + '/').html('Details');
row.append($('<td>').append(link));
body.append(row);
}
table.append(body);
div.append(table);
$('#resultbrowsercontainer').append(div);
}
});
return false;
});
});

Simply remove the target attribute and then it will open inside itself:
<!--I would like to avoid opening a new window-->
link = $('<a>').attr('href', '/result_details/' + data[i].result_id + '/').html('Details');

div sort not working when div generated dynamically

I'm trying to sort a list of divs with the properties shown by particular attributes (gender, level, name etc) using the following script:
html:
<div id="sortThis" class="col-xs-12 alert-container">
<div id="1" class="container-element sortable box box-blue" data-gender="1" data-level="4" data-name="AAA"> <h3>AAA</h3><div class="panel-body">AAA is resp</div>
</div>
<div id="2" class="container-element sortable box box-pink" data-gender="2" data-level="3" data-name="DDD"><h3>DDD</h3><div class="panel-body">DDD is a s</div>
</div>
<div id="3" class="container-element sortable box box-blue" data-gender="1" data-level="2" data-name="FFF"><h3>FFF</h3><div class="panel-body">FFF has mad</div>
</div>
<div id="4" class="container-element sortable box box-pink" data-gender="2" data-level="4" data-name="CCC"><h3>CCC</h3><div class="panel-body">CCC has ma</div>
</div>
<div id="5" class="container-element sortable box box-pink" data-gender="2" data-level="2" data-name=EEE><h3>EEE</h3><div class="panel-body">EEE is a f</div>
</div>
<div id="6" class="container-element sortable box box-blue" data-gender="1" data-level="3" data-name="BBB"><h3>BBB</h3><div class="panel-body">BBB is an ou</div>
</div>
</div>
<button id="sLevel" class="LbtnSort">Sort by Level</button><br/>
<button id="sGender" class="GbtnSort">Sort by Gender</button><br/>
js:
var LdivList = $(".box");
LdivList.sort(function(a, b){
return $(a).data("level")-$(b).data("level")
});
var GdivList = $(".box");
GdivList.sort(function(a, b){
return $(a).data("gender")-$(b).data("gender")
});
/* sort on button click */
$("button.LbtnSort").click(function() {
$("#sortThis").html(LdivList);
});
/* sort on button click */
$("button.GbtnSort").click(function() {
$("#sortThis").html(GdivList);
});
when the .sortable divs are static, the sort works fine, as this jfiddle shows, however if the contents of the #sortable div (i.e. .sortable divs) are dynamically generated (in this case as the result of a form submit), when the sort button is pressed, the entire contents of the #sortable div disappears, and I can't seem to get it to work.
Any help or suggestions would be appreciated.
edit: The code for dynamic generation of the list is as follows - effectively it's an AXAX form submit that pulls data from a sorted list of items and outputs them.
$('#formStep2').submit(function(event) {
// get the form data
var studentArray = [];
$(".listbox li").each(function() {
studentArray.push({
'name': ($(this).text()),
'gender': ($(this).closest('ol').attr('id')).substr(0, 1),
'level': ($(this).closest('ol').attr('id')).substr(2, 3),
'topic': ($('input[name=topic]').val())
})
});
var studentString = JSON.stringify(studentArray);
console.log(studentString);
var formData = {
'students': studentString,
};
// process the form
$.ajax({
type: 'POST', // define the type of HTTP verb we want to use (POST for our form)
url: 'process_step2.php', // the url where we want to POST
data: formData, // our data object
dataType: 'json', // what type of data do we expect back from the server
encode: true
})
// using the done promise callback
.done(function(data) {
if (!data.success) {
// error handling to go here.....
} else {
$('.alert-container').empty();
var obj = JSON.parse(data.message);
//sort the array alphabetically by name (default status)
var test = obj.sort(function(a,b){
var lccomp = a.name.toLowerCase().localeCompare(b.name.toLowerCase());
return lccomp ? lccomp : a.name > b.name ? 1 : a.name < b.name ? -1 : 0;
});
console.log(test);
var i=0;
test.forEach(function(st) {
console.log(st['name']);
var gen = (st['gender'] == 1) ? "blue" : (st['gender'] == 2) ? "pink" : NULL;
$('.alert-container').append('<div id="' + (i+1) + '" class="container-element sortable box box-' + gen + '" data-gender="' + st['gender'] + '" data-level="' + st['level'] + '" data-name="' + st['name'] + '"><h3>' + st['name'] + '</h3><div class="panel-body"><div class="col-xs-9"><i class="fa fa-quote-left fa-3x fa-pull-left fa-' + gen + '" aria-hidden=:true"></i>' + st['comment'] + '</div></div></div>');
i++;
});
// jump to the next tab
var $active = $('.wizard .nav-tabs li.active');
$active.next().removeClass('disabled');
nextTab($active);
}
})
// using the fail promise callback
.fail(function(data) {
// show any errors
// best to remove for production
console.log(data);
});
// stop the form from submitting the normal way and refreshing the page
event.preventDefault();
});

You are defining LdivList and GdivList inline with your code so they are defined on DOM ready. You have to wrap the definition of those inside a function and call it on click:
$(document).ready(function(){
$("button.LbtnSort").click(function() {
$("#sortThis").html(GenerateLdivList);
});
/* sort on button click */
$("button.GbtnSort").click(function() {
$("#sortThis").html(GenerateGdivList());
});
});
function GenerateLdivList(){
var LdivList = $(".box");
LdivList.sort(function(a, b){
return $(a).data("level")-$(b).data("level")
});
}
function GenerateGdivList(){
var GdivList = $(".box");
GdivList.sort(function(a, b){
return $(a).data("gender")-$(b).data("gender")
});
}

As #theduke said, the lists are probably empty at the time you sort them. Here's a simple change that will read and sort the lists when you click the buttons instead. (Not tested.)
var LdivList = function () {
return $(".box").sort(function(a, b){
return $(a).data("level")-$(b).data("level")
});
};
var GdivList = function () {
return $(".box").sort(function(a, b){
return $(a).data("gender")-$(b).data("gender")
});
};
/* sort on button click */
$("button.LbtnSort").click(function() {
$("#sortThis").html(LdivList());
});
/* sort on button click */
$("button.GbtnSort").click(function() {
$("#sortThis").html(GdivList());
});