Develop Reference

Iterating through an array nested inside of an object

thank you for the help in advance! Please forgive me if this is a stupid question as I a JS noobie.
I am trying to cycle through an array of URL's that I have nested inside of an object. What I am expecting to happen is for the url's (which are google maps) to show up on my website and for the person using my website to be able to click back and forth between the different map URL's. Right now what's happening is the last item (a google maps url) of myCities.index is being properly displayed, but when I click my previous and next buttons it is going to a blank page. I have looked at my JS console and there are no visible errors there. Can anyone give me some advice as to how to fix this? My code is as follows.
const myCities = {
index:
[url1, url2, url3]
}
const prevButton = document.querySelector('.prevBtn');
const nextButton = document.querySelector('.nextBtn');
const map = document.getElementById("myCitiesss");
nextButton.addEventListener('click', nextCity);
prevButton.addEventListener('click', prevCity);
function prevCity() {
myCities.index--;
updateSrc();
checkButtons();
}
function nextCity() {
myCities.index++;
updateSrc();
checkButtons();
}
function updateSrc() {
map.src = myCities.index;
}
function checkButtons() {
prevButton.disabled = false;
nextButton.disabled = false;
if (myCities.index === 2) {
nextButton.disabled = true;
}if (myCities.index === 0) {
prevButton.disabled = true;
}
}
updateSrc();
checkButtons();

The problem is you're treating myCities.index as both the container of your data and as a counter (hence you're running incrementation/decrementation operations on it).
The counter should be a separate variable.
const myCities = [url1, url2, url3]; //<-- can now be a flat array
let index = 0; //<-- this is our counter, i.e. tracker
The relevant code changes are then: (I also took the opportunity to demonstrate some optimisations and efficiencies you can make)
nextButton.addEventListener('click', () => nextPrevCity('next'));
prevButton.addEventListener('click', () => nextPrevCity('prev'));
function nextPrevCity(which) { //<-- one function to handle both next and prev
which == 'next' ? index++ : index--;
map.src = myCities[index];
checkButtons();
}
function checkButtons() {
prevButton.disabled = false;
nextButton.disabled = false;
if (index === myCities.length - 1) //<-- check against array length, not fixed number 2
nextButton.disabled = true;
if (!index) //<-- because 0 is a falsy value, so same as "if (index === 0)"
prevButton.disabled = true;
}
[ -- EDIT -- ]
Forgot the following at the bottom of the code:
map.src = myCities[0];
checkButtons();

JavaScript - Issues recovering a map in an object after being saved in localStorage

I've been dealing with this for some time. I've a list of sections in which the user checks some checkboxes and that is sent to the server via AJAX. However, since the user can return to previous sections, I'm using some objects of mine to store some things the user has done (if he/she already finished working in that section, which checkboxes checked, etc). I'm doing this to not overload the database and only send new requests to store information if the user effectively changes a previous checkbox, not if he just starts clicking "Save" randomly. I'm using objects to see the sections of the page, and storing the previous state of the checkboxes in a Map. Here's my "supervisor":
function Supervisor(id) {
this.id = id;
this.verif = null;
this.selections = new Map();
var children = $("#ContentPlaceHolder1_checkboxes_div_" + id).children().length;
for (var i = 0; i < children; i++) {
if (i % 2 == 0) {
var checkbox = $("#ContentPlaceHolder1_checkboxes_div_" + id).children()[i];
var idCheck = checkbox.id.split("_")[2];
this.selections.set(idCheck, false);
}
}
console.log("Length " + this.selections.size);
this.change = false;
}
The console.log gives me the expected output, so I assume my Map is created and initialized correctly. Since the session of the user can expire before he finishes his work, or he can close his browser by accident, I'm storing this object using local storage, so I can change the page accordingly to what he has done should anything happen. Here are my functions:
function setObj(id, supervisor) {
localStorage.setItem(id, JSON.stringify(supervisor));
}
function getObj(key) {
var supervisor = JSON.parse(localStorage.getItem(key));
return supervisor;
}
So, I'm trying to add to the record whenever an user clicks in a checkbox. And this is where the problem happens. Here's the function:
function checkboxClicked(idCbx) {
var idSection = $("#ContentPlaceHolder1_hdnActualField").val();
var supervisor = getObj(idSection);
console.log(typeof (supervisor)); //Returns object, everythings fine
console.log(typeof (supervisor.change)); //Returns boolean
supervisor.change = true;
var idCheck = idCbx.split("_")[2]; //I just want a part of the name
console.log(typeof(supervisor.selections)); //Prints object
console.log("Length " + supervisor.selections.size); //Undefined!
supervisor.selections.set(idCheck, true); //Error! Note: The true is just for testing purposes
setObj(idSection, supervisor);
}
What am I doing wrong? Thanks!

Please look at this example, I removed the jquery id discovery for clarity. You'll need to adapt this to meet your needs but it should get you mostly there.
const mapToJSON = (map) => [...map];
const mapFromJSON = (json) => new Map(json);
function Supervisor(id) {
this.id = id;
this.verif = null;
this.selections = new Map();
this.change = false;
this.selections.set('blah', 'hello');
}
Supervisor.from = function (data) {
const id = data.id;
const supervisor = new Supervisor(id);
supervisor.verif = data.verif;
supervisor.selections = new Map(data.selections);
return supervisor;
};
Supervisor.prototype.toJSON = function() {
return {
id: this.id,
verif: this.verif,
selections: mapToJSON(this.selections)
}
}
const expected = new Supervisor(1);
console.log(expected);
const json = JSON.stringify(expected);
const actual = Supervisor.from(JSON.parse(json));
console.log(actual);
If you cant use the spread operation in 'mapToJSON' you could loop and push.
const mapToJSON = (map) => {
const result = [];
for (let entry of map.entries()) {
result.push(entry);
}
return result;
}
Really the only thing id change is have the constructor do less, just accept values, assign with minimal fiddling, and have a factory query the dom and populate the constructor with values. Maybe something like fromDOM() or something. This will make Supervisor more flexible and easier to test.
function Supervisor(options) {
this.id = options.id;
this.verif = null;
this.selections = options.selections || new Map();
this.change = false;
}
Supervisor.fromDOM = function(id) {
const selections = new Map();
const children = $("#ContentPlaceHolder1_checkboxes_div_" + id).children();
for (var i = 0; i < children.length; i++) {
if (i % 2 == 0) {
var checkbox = children[i];
var idCheck = checkbox.id.split("_")[2];
selections.set(idCheck, false);
}
}
return new Supervisor({ id: id, selections: selections });
};
console.log(Supervisor.fromDOM(2));
You can keep going and have another method that tries to parse a Supervisor from localStorageand default to the dom based factory if the localStorage one returns null.

Javascript basic loop help - basic

Im learning Javascript now and I got a question that's been bugging me!
So, all I needed to do here is to type a color on this input box, click the button and change the headline to the color typed only if that typed color is in the array specified in the variable.
My code is half working... it does check if whatever color typed is inside the array, but the alert button pops up each time, is there a way to make the alert pop up only if the color typed isn't in the array please?
Working code: https://codepen.io/anon/pen/ddPWLP
Javascript code:
const myHeading = document.getElementById('myHeading');
const myButton = document.getElementById('myButton');
const myTextInput = document.getElementById('myTextInput');
var colors = ["red", "black", "blue"];
myButton.addEventListener('click', () => {
for (var i=0; i<colors.length; i++){
if (myTextInput.value === colors[i]){
myHeading.style.color = myTextInput.value
} else {
alert("no color")
}
}
});

Don't do it inside the loop. Use a variable to flag when you find a match, and then after the loop check that flag and display the alert accordingly. Try this:
myButton.addEventListener('click', () => {
var found = false;
for (var i = 0; i < colors.length; i++) {
if (myTextInput.value === colors[i]) {
myHeading.style.color = myTextInput.value
found = true;
}
}
if (!found)
alert("no color");
});
By the way, you don't need a loop for that. You can simply use the indexOf() methods. If the value exists in the array, it returns its index, otherwise it returns -1. Try this:
myButton.addEventListener('click', () => {
if (colors.indexOf(myTextInput.value) > -1)
myHeading.style.color = myTextInput.value
else
alert("no color");
});

Storin a variable with many id's in array

var arrayOfId[] = $scope.rep.Selected.id;
I have this code. My question is if I had a some id's in $scope...Selected.id and then I make this (code) all these id's will be in every other array or in one array?

$scope.delIt = function () {
if ($scope.rep.Selected > 0) {
$scope.rep.Selected = true;
} else {
$scope.rep.Selected = false
}
var arrayOfId [] = $scope.rep.Selected.id;
for(i=0; i<=arrayOfId[i]; i++){
$http.delete("http://localhost:3000/users/" +arrayOfId[]);
}
}
This is full code. I wanted to send request every single id wich is stored in $scope.rep.Selected.id

Advanced search/queue array collection question

I have a pretty large number of objects "usrSession" I store them in my ArrayCollection usrSessionCollection.
I'M looking for a function that returns the latest userSessions added with a unique userID. So something like this:
1.
search the usrSessionCollection and only return one userSessions per userID.
2.
When it has returned x number of userSessions then deleted them from the usrSessionCollection
I'M stuck - would really love some code that can help me with that.
function ArrayCollection() {
var myArray = new Array;
return {
empty: function () {
myArray.splice(0, myArray.length);
},
add: function (myElement) {
myArray.push(myElement);
}
}
}
function usrSession(userID, cords, color) {
this.UserID = userID;
this.Cords = cords;
this.Color = color;
}
usrSessionCollection = new ArrayCollection();
$.getJSON(dataurl, function (data) {
for (var x = 0; x < data.length; x++) {
usrSessionCollection.add(new usrSession(data[x].usrID.toString(), data[x].usrcords.toString() ,data[x].color.toString());
}
});
Thanks.

The biggest issue is that you have made the array private to the outside world. Only methods through which the array can be interacted with are add and empty. To be able to search the array, you need to either add that functionality in the returned object, or expose the array. Here is a modified ArrayCollection:
function ArrayCollection() {
var myArray = new Array;
return {
empty: function () {
myArray.splice(0, myArray.length);
},
add: function (myElement) {
myArray.push(myElement);
},
getAll: function() {
return myArray;
}
}
}
Now to get the last N unique session objects in usrSessionCollection, traverse the sessions array backwards. Maintain a hash of all userID's seen so far, so if a repeated userID comes along, that can be ignored. Once you've collected N such user sessions or reached the beginning of the array, return all collected sessions.
usrSessionCollection.getLast = function(n) {
var sessions = this.getAll();
var uniqueSessions = [];
var addedUserIDs = {}, session, count, userID;
for(var i = sessions.length - 1; i >= 0, uniqueSessions.length < n; i--) {
session = sessions[i];
userID = session.userID;
if(!addedUserIDs[userID]) {
uniqueSessions.push(session);
addedUserIDs[userID] = true;
}
}
return uniqueSessions;
}
I wouldn't combine the delete step with the traversal step, just to keep things simple. So here's the remove method that removes the given session from the array. Again, it's better to modify the interface returned by ArrayCollection rather than tampering with the sessions array directly.
function ArrayCollection(..) {
return {
..,
remove: function(item) {
for(var i = 0; i < myArray.length; i++) {
if(item == myArray[i]) {
return myArray.splice(i, 1);
}
}
return null;
}
};
}
Example: Get the last 10 unique sessions and delete them:
var sessions = usrSessionCollection.getLast(10);
for(var i = 0; i < sessions.length; i++) {
console.log(sessions[i].UserID); // don't need dummy variable, log directly
usrSessionCollection.remove(sessions[i]);
}
See a working example.

You made your array private, so you can't access the data, except adding a new element or removing them all. You need to make the array public, or provide a public interface to access the data. Like first(), next() or item(index).
Then you can add a search(userID) method to the usrSessionCollection, which uses this interface to go through the elements and search by userID.
UPDATE: this is how I would do it: - See it in action. (click preview)
// user session
function userSession(userID, cords, color) {
this.UserID = userID;
this.Cords = cords;
this.Color = color;
}
// a collection of user sessionions
// a decorated array basically, with
// tons of great methods available
var userSessionCollection = Array;
userSessionCollection.prototype.lastById = function( userID ) {
for ( var i = this.length; i--; ) {
if ( this[i].UserID === userID ) {
return this[i];
}
}
// NOTE: returns undefined by default
// which is good. means: no match
};
// we can have aliases for basic functions
userSessionCollection.prototype.add = Array.prototype.push;
// or make new ones
userSessionCollection.prototype.empty = function() {
return this.splice(0, this.length);
};
//////////////////////////////////////////////////////
// make a new collection
var coll = new userSessionCollection();
// put elements in (push and add are also available)
coll.add ( new userSession(134, [112, 443], "#fffff") );
coll.push( new userSession(23, [32, -32], "#fe233") );
coll.push( new userSession(324, [1, 53], "#ddddd") );
// search by id (custom method)
var search = coll.lastById(134);
if( search ) {
console.log(search.UserID);
} else {
console.log("there is no match");
}
// empty and search again
coll.empty();
search = coll.lastById(134);
if( search ) {
console.log(search.UserID);
} else {
console.log("there is no match");
}