We Keep Coding

react throws type error for undefined object before ternary can check if object is undefined

LONG STORY SHORT: I would like for it to load the object in the nested array IF it is not equal to undefined but react throws typeError
I have this component that takes props from a parent component. Essentially I have an array that contains chat information and when I try to access it in this child component I get some very strange behaviour.
for example if I console log(props.conversations) I get my array which looks like this: conversations[{host, members[{ username }], log[{ author, content, timestamp }]}].
if I console log (props.conversations[0]) ill get the first object in that array. But if I console log (props.conversations[0].log) I get undefined. And thats fine because at the start the state will not be defined or contain anything, so I put a ternary operator as shown below in the code props.conversations[props.index].log[0] == null ?
but all i get is TypeError: Cannot read property 'log' of undefined at the ternary function.
Maybe I am not understanding this correctly or maybe it how react functions?
Again I would like for it to load the object in the nested array IF it is not equal to undefined.
Highly appreciate the help. The most important part is the friends component. I only show the other ones to show the state being passed down.
function Friends(props) {
console.log(props.conversations[props.index]);
return (
<div className="friend">
<img className="friendavatar" src={require("./static/bobby.jpg")}></img>
<div className="friendname">{props.username}</div>
<span className="iswatchingtitle"> is watching <strong>{props.watching}</strong></span>
<div className="friendchat" onClick={props.togglechat}>
{props.conversations[props.index].log[0] == null ?
<div>undefined</div>
:
<div>defined!</div>
}
</div>
</div>
)
}
social component
function Social(props) {
return (
<div>
<div className="userquickdash row">
<div className="usernamedash">{props.username}</div>
<div className="logout"><a href="/users/logout" onClick={props.fetchlogout}>logout</a></div>
</div>
<div>
<form className="search-form-flex" method="GET" action="/search">
<input className="user-search" id="search" type="search" placeholder=" Search users..." name="usersearch"></input>
</form>
</div>
<div className='friendchatcontainer' refs='friendchatcontainer'>
{/* Append friends from social bar state (props.friends). For each friend return appropriate object info to build Friends div using Friends(props) function above. */}
{props.friends.map(function(friend, index) {
// Shortens length of video title if length of string is over 48.
let friendWatching = function friendWatchingLengthSubstring() {
if (friend.watching.length > 57) {
let friendWatching = friend.watching.substring(0, 54) + '...';
return friendWatching;
} else {
friendWatching = friend.watching;
return friendWatching;
}
};
return (
<Friends username={friend.username}
watching={friendWatching()}
key={index}
index={index}
togglechat={props.togglechat}
conversations={props.conversations}
/>
)
})}
</div>
</div>
)
}
socialbar component
class Socialbar extends Component {
constructor(props) {
super(props);
this.state = { isLoggedIn: (cookies.get('loggedIn')),
sidebarximgSrc: sidebarcloseimg,
sidebarStatus: 'open',
username: cookies.get('loggedIn'),
friends: friends,
users: {},
conversations: [],
};
}
// function to run when mongodb gets information that state has changed.
// test if the current state is equal to new object array.
// then do something.
appendFriends() {
}
componentDidMount() {
if (this.state.sidebarStatus === 'open') {
document.getElementsByClassName('maindash')[0].classList.add('maindashwide');
this.openSideBar();
} else {
document.getElementsByClassName('maindash')[0].classList.remove('maindashwide');
this.closeSideBar();
}
// check for user logged in cookie, if true fetch users.
if (this.state.isLoggedIn) {
this.fetchUsers();
}
this.getFriendConversations();
};
getFriendConversations() {
// build loop function that updates state for conversations based on length of friends array in state.
var conversationsArray = this.state.conversations;
for (var i = 0; i < friends.length; i++) {
console.log(aconversationbetweenfriends[i]);
conversationsArray.push(aconversationbetweenfriends[i]);
}
this.setState({conversations: conversationsArray});
}
render() {
let sidebar;
const isLoggedIn = this.state.isLoggedIn;
if (!isLoggedIn) {
sidebar = <Login />
} else {
sidebar = <Social username={this.state.username} friends={this.state.friends} fetchlogout={this.fetchlogout} togglechat={this.togglechat} conversations={this.state.conversations} />
}
return (
<div>
<div className="sidebar sidebar-open" ref="sidebar">
<div className="sidebarcontainer">
{sidebar}
</div>
</div>
<div className="sidebarx sidebarxopen" ref="sidebarx" onClick={this.toggleSideBar}>
<img className="sidebaropenimg" src={this.state.sidebarximgSrc} ref='sidebarximg'></img>
</div>
</div>
);
}
};

It is not a good idea to access the element directly before validation.
Use something like this:
props.conversations[props.index] && props.conversations[props.index].log[0]
Tip: User object destructuring and default props.

You need to compare for undefined like this :
{props.conversations[props.index].log[0] === undefined ?
<div>undefined</div>
:
<div>defined!</div>
}
Also, You can go to below link for sandbox running example.
Sandbox link for example to show how you should check for undefined

Hi first of all check your {props.index} print this value. if it is proper then try this out.
{
props.conversations[props.index] ?
props.conversations[props.index].log[0] ? <div>defined!</div>:<div>Undefined</div>
:
<div>Undefined</div>
}
This will check if props.conversations[props.index] is defined then and then only try to process props.conversations[props.index].log[0]. So you will not get TypeError: Cannot read property 'log' of undefined at the ternary function.

sessionStorage return null

Im trying to achieve this piece of code but in my console it says thing is null which is weird because when I look in the console, sessionStorage isn't empty...
$(".btn-alert").click(function(){
var identifierOfSpan = $(this > "span").text();
for(var prop in sessionStorage){
var thing = JSON.parse(sessionStorage.getItem(prop))
if(thing.id == identifierOfSpan){
sessionStorage.removeItem(prop);
}
}
$(this).closest(".voyages").remove();
if(sessionStorage.length == 0){
alert("Message!");
location.href="reservation.html"
}
});
the button is supposed to delete the div and the sessionStorage item which looks like this
Html :
<div class="voyages">
<button class="btn btn-alert btn-md mr-2" tabindex="-1">delete the flight</button>
<span>ID : 4224762</span>
<div class="infos">
<img src="img/angleterre.jpg" alt="maroc">
<div>
<ul>
<li><h5>Angleterre, Londres (LON)</h5></li>
<li><h5>2 adulte(s)</h5></li>
<li><h5> Aucun enfants </h5></li>
<li><h5>Type : Couple</h5></li>
</ul>
</div>
</div>
<hr>
<h3>Options</h3>
<ul>
<li>voiture : 0</li>
<li>Hotel : 0 </li>
</ul>
<hr>
<h3>Prix :3713$</h3>

If I'm reading your question correctly, you want to...
Click on a button
Find the first sibling <span> element and parse a number out of its text content
Remove all sessionStorage items (JSON serialized objects) with matching id properties
For the ID, I highly recommend adding some data directly to the <button> to help you identify the right record. If you can, try something like
<button class="btn btn-alert btn-md mr-2" data-voyage="4224762"...
Try something like this
$('.btn-alert').on('click', function() {
const btn = $(this)
const id = btn.data('voyage')
// or, if you cannot add the "data-voyage" attribute
const id = btn.next('span').text().match(/\d+$/)[0]
// for index-based removal, start at the end and work backwards
for (let i = sessionStorage.length -1; i >= 0; i--) {
let key = sessionStorage.key(i)
let thing = JSON.parse(sessionStorage.getItem(key))
if (thing.id == id) {
sessionStorage.removeItem(key)
}
}
// and the rest of your code
btn.closest(".voyages").remove();
if(sessionStorage.length === 0) {
alert("Message!");
location.href = 'reservation.html'
}
})
The problem with using a for..in loop on sessionStorage is that you not only get any item keys added but also
length
key
getItem
setItem
removeItem
clear

element in my $scope variable won't get display

I just deployed a website to test in "production" but when i try to go to the website some of my computer won't see one the results of my ng-repeat and some will see. If I go to the website when there's nothing displayed I look at the source code and I see the ng-repeat with each object of my array, but no html output on the screen. Here some of my code when I load my controller:
/**
* Function that send a request to get a list of posts.
* #return {Function} A promise.
*/
function retrievePosts() {
var defered = $q.defer();
// If the user is logged in we do a search by country, otherwise we get all the posts.
if($rootScope.user !== null && $rootScope.user !== undefined) {
PostService.searchPost({ countries: [$rootScope.user.country] }, function(err, posts) {
if(err) {
defered.reject(err);
}
else if(posts && posts.length > 0) {
defered.resolve(posts);
}
// If the previous condition is not true, we try to get all the posts, since the search by country didn't work.
else {
PostService.getAllPosts(function(err, posts2) {
if(err) {
defered.reject(err);
} else {
defered.resolve(posts2);
}
});
}
});
} else {
PostService.getAllPosts(function(err, posts) {
if(err) {
defered.reject(err);
}
else {
defered.resolve(posts);
}
});
}
return defered.promise;
}
This function is used to get an array of JSON posts object. Then I do a q.all like this:
$q.all([retrieveManufacturer(), retrieveCategories(), retrievePosts(), getTotalPosts(), retrieveGalleryPosts()]).then(function(results) {
$scope.manufacturers = results[0];
$scope.categories = results[1];
// Here we must cache the result and slice it, so that angular doesn't render
// a tone of post but 10 at a time.
postCache = results[2];
$scope.numberOfPostsToShow = 10;
$scope.posts = postCache.slice(0, $scope.numberOfPostsToShow);
// Some code to display the proper amount of post for each category.
var i = -1;
var max = results[3].length;
var groupedPostsCount = { };
var group;
while(++i < max) {
group = results[3][i];
// "_id" contains the name of the category.
groupedPostsCount[group._id] = group.count;
}
if(Object.keys(groupedPostsCount).length > 0){
$scope.categoriesPostCount = groupedPostsCount;
}
$scope.galleryPosts = results[4];
// Prepare the $scope.galleryPosts to be bound with posts.
buildGallery($scope.galleryPosts);
}, function(err) {
console.log(err);
});
Every task in $q.all gets executed and they all get resolved. I see them in my HTML like the categories, manufacturers, etc... Results[2] which are the array of posts are not null they really do have 500 posts in them. I try to call $scope.$apply() after buildGallery() method call, but nothing work. If I print {{ posts }} anywhere in my html i see the array of posts. But when they are in that ng-repeat:
<div class="ad-container" ng-repeat="post in posts" ng-click="viewPostDetails(post)">
<div class="ad-picture">
<table class="wrapper">
<tr>
<td><img ng-src="img/175/{{ post.mainImageName || post.imgUrls[0] }}" alt="No image provided"/></td>
</tr>
</table>
</div>
<div class="ad-info">
<span class="ad-info-title">{{ post.title }}</span>
<span class="ad-info-price">{{ post.country == 'Canada' ? (post.price | currency : "CA$") : (post.price | currency : "US$") }}</span>
<br />
<span>{{ post.country }}, {{ post.province }}, {{ post.createdAt | date }}</span>
<p>{{ post.description }}</p>
</div>
</div>
Of course this code is inside a div that has a controller bound to it.Like I said, it's really weird. On my development computer everything works perfectly, but some of the computers of my friend did work and others didn't. Here's the link to the website www.firearmsbin.com maybe the problem will occur on your computer. I tried on firefox, firefox for dev, edge, chrome and IE11.
Thanks.

I found out that it was adblock who was not displaying my div which as the class "ad-container". So every class in css that contains "ad" word get block.

How to force binding re-evaluate or re-rendering in Aurelia

I am starting with a simple TODO app with Aurelia, RethinkDB & Socket.IO. I seem to have problem with re-rendering or re-evaluating an object that is changed through Socket.IO. So basically, everything works good on the first browser but doesn't get re-rendered in the second browser while displaying the object in the console does show differences in my object. The problem is only on updating an object, it works perfectly on creating/deleting object from the array of todo items.
HTML
<ul>
<li repeat.for="item of items">
<div show.bind="!item.isEditing">
<input type="checkbox" checked.two-way="item.completed" click.delegate="toggleComplete(item)" />
<label class="${item.completed ? 'done': ''} ${item.archived ? 'archived' : ''}" click.delegate="$parent.editBegin(item)">
${item.title}
</label>
<i class="glyphicon glyphicon-trash"></i>
</div>
<div show.bind="item.isEditing">
<form submit.delegate="$parent.editEnd(item)">
<input type="text" value.bind="item.title" blur.delegate="$parent.editEnd(item)" />
</form>
</div>
</li>
</ul>
NodeJS with RethinkDB changefeeds
// attach a RethinkDB changefeeds to watch any changes
r.table(config.table)
.changes()
.run()
.then(function(cursor) {
//cursor.each(console.log);
cursor.each(function(err, item) {
if (!!item && !!item.new_val && item.old_val == null) {
io.sockets.emit("todo_create", item.new_val);
}else if (!!item && !!item.new_val && !!item.old_val) {
io.sockets.emit("todo_update", item.new_val);
}else if(!!item && item.new_val == null && !!item.old_val) {
io.sockets.emit("todo_delete", item.old_val);
}
});
})
.error(function(err){
console.log("Changefeeds Failure: ", err);
});
Aurelia code watching Socket.on
// update item
socket.on("todo_update", data => {
let pos = arrayFindObjectIndex(this.items, 'id', data.id);
if(pos >= 0) {
console.log('before update');
console.log(this.items[pos]);
this.items[pos] = data;
this.items[pos].title = this.items[pos].title + ' [updated]';
console.log('after update');
console.log(this.items[pos]);
}
});
// create item, only add the item if we don't have it already in the items list to avoid dupes
socket.on("todo_create", data => {
if (!_.some(this.items, function (p) {
return p.id === data.id;
})) {
this.items.unshift(data);
}
});
// delete item, only delete item if found in items list
socket.on("todo_delete", data => {
let pos = arrayFindObjectIndex(this.items, 'id', data.id);
if(pos >= 0) {
this.items.splice(pos, 1);
}
});
The socket.on("todo_update", ...){} is not making the second browser re-render but showing the object in the console before/after update does show differences in the object itself. I even changed the todo title property and that too doesn't get re-rendered.
How can I get Aurelia to re-render in my second browser with the new object properties? Don't be too hard on me, I'm learning Aurelia/RethinkDB/NodeJS/Socket.IO all the same time...

Aurelia observes changes to the contents of an array by overriding the array's mutator methods (push, pop, splice, shift, etc). This works well for most use-cases and performs really well (no dirty-checking, extremely lightweight in terms of memory and cpu). Unfortunately this leaves one way of mutating an array that aurelia can't "see": indexed assignment... eg myArray[6] = 'foo'. Since no array methods were called, the binding system doesn't know the array changed.
In your case, try changing this:
// update item
socket.on("todo_update", data => {
let pos = arrayFindObjectIndex(this.items, 'id', data.id);
if(pos >= 0) {
console.log('before update');
console.log(this.items[pos]);
this.items[pos] = data; // <-- change this to: this.items.splice(pos, 1, data);
this.items[pos].title = this.items[pos].title + ' [updated]';
console.log('after update');
console.log(this.items[pos]);
}
});

How do I make json get to work in angularJS?

I followed information on this answer
But it doesn't work in my situation.
Chrome Inspector console says "ReferenceError: dataResponse is not defined"
maybe that is the problem?
I am trying to GET this JSON from url:
[{"app_id":1,"app_name":"oh yeeah","app_description":"desc","app_price":111,"is_activated":false,"video":"videolink"},{"app_id":2,"app_name":"oh yeaaaeah","app_description":"ewaewq","app_price":222,"is_activated":false,"video":"fuck off"},{"app_id":3,"app_name":"oh yeaaaeah","app_description":"ewaewq","app_price":333,"is_activated":false,"video":"fuck off"}]
This is my javascript code
var appstore = angular.module('appstore', []);
appstore.service('dataService', function($http) {
delete $http.defaults.headers.common['X-Requested-With'];
this.getData = function(callbackFunc) {
$http({
method: 'GET',
url: '/administrator/components/com_apps/loadAppsJson.php'
}).success(function(data){
callbackFunc(data);
}).error(function(){
alert("error");
});
}
});
appstore.controller('app_Ctrl', function($scope, dataService) {
$scope.apps = [
{app_id:1, app_name:'oh yeah', app_description:'$app_description', app_price:111, is_activated:false, video:'$videolink'},
{app_id:2, app_name:'oh yeah', app_description:'$app_description', app_price:111, is_activated:false, video:'$videolink'},
{app_id:3, app_name:'oh yeah', app_description:'$app_description', app_price:111, is_activated:false, video:'$videolink'},
];
//$scope.apps = null;
dataService.getData(function(dataResponse) {
$scope.apps = dataResponse;
alert(dataResponse);
});
console.log(dataResponse);
console.log($scope.apps);
//get images thumbs
for(app = 0; app <= $scope.apps.length-1; app++) {
$scope.apps[app].thumb = ("000" + $scope.apps[app].app_id).slice(-3);
}
//separate apps to columns
var columns = [];
for (var i = 0; i < $scope.apps.length; i++ ) {
if (i % 3 == 0) columns.push([]);
columns[columns.length-1].push($scope.apps[i]);
}
$scope.columns = columns;
});
My HTML view
<div ng-controller="app_Ctrl">
<div class="row"></div>
<div class="row">
<div class="row" ng-repeat="apps in columns">
<div id="app_id_{{ app.app_id }}" class="col-lg-4" ng-repeat="app in apps | filter:search">
<div class="thumbnail" ng-class="app.is_activated ? 'activated' : ''">
<!-- -->
<img ng-src="/images/apps/app_images/{{ app.thumb }}_thumb.jpg" alt="{{ app.app_name }}" title="{{ app.app_name }}">
<div class="caption">
<h3>{{ app.app_name }}</h3>
<p class="app_price">{{ app.app_price }} €</p>
<div style="clear:both;"></div>
<p class="app_card_description">{{ app.app_description | limitTo:100 }}...</p>
Info
Video <span class="glyphicon glyphicon-facetime-video"></span>
{{ app.is_activated ? 'Aktivované' : 'Aktivovať' }}
</div>
</div>
</div>
</div>

To elaborate on what #Mritunjay said in the comments; review this code with comments:
dataService.getData(
// this is your callback function which has an argument for dataResponse
// the dataResponse variable will only be defined within the Call back function
function(dataResponse) {
$scope.apps = dataResponse;
alert(dataResponse);
// The Curly Brackets that follow mark the end of the callback handler method
});
// This log statement is not in the callback handler and there is no defined dataResponse variable which is probably why you got an error in the console
console.log(dataResponse);
You can fix this by moving the dataResponse log into the callback method, like this:
dataService.getData(function(dataResponse) {
$scope.apps = dataResponse;
alert(dataResponse);
console.log(dataResponse);
});
There appear to be other problems with your code, in that you are trying to access $scope.apps before the data is returned; which will hinder your processing. Easiest approach would be to move that processing into the result handler:
// define $scope.columns outside of the result handler
$scope.columns = [];
// call to method in service
dataService.getData(function(dataResponse) {
$scope.apps = dataResponse;
alert(dataResponse);
console.log(dataResponse);
// inside the result handler; you run this code after $scope.apps is defined:
for(app = 0; app <= $scope.apps.length-1; app++) {
$scope.apps[app].thumb = ("000" + $scope.apps[app].app_id).slice(-3);
}
//separate apps to columns
var columns = [];
for (var i = 0; i < $scope.apps.length; i++ ) {
if (i % 3 == 0) columns.push([]);
columns[columns.length-1].push($scope.apps[i]);
}
$scope.columns = columns;
});

That's what promises and asynchronous calls are all about.
console.log(dataResponse);
console.log($scope.apps);
The first one won't work because dataResource is a private variable and not part of the same scope you're trying to print.
The second one won't work either because that get's populated at future time (after X seconds), after the $http request is finished so it will only be availableat that point.
One way to do something after the object is populated is to use
$scope.$watch("apps", function (){
// do stuff
});