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Get index of array is not working

I am learning Vue and I am trying to access a string in an array by it's index, but I always get an error when trying to read the string. Here's my code:
var vm = new Vue({
el: '#top',
data: {
Cars: [],
DefaultCarList: [],
AddedCars: [],
SelectedCar: ''
},
methods: {
addCar: function(car) {
var addedCarCount = this.AddedCars.length;
var defaultCarCount = this.DefaultCarList.length;
var containsCar = function () {
for (var i = 0; i < addedCarCount; i++)
{
if (this.AddedCars[i] === car) // error here
{
return true;
}
}
return false;
}
var carIsValid = function() {
for(var i = 0; i < defaultCarCount; i++)
{
if(this.DefaultCarList[i] === this.SelectedCar) // error here
{
return true;
}
}
return false;
}
if (containsCar() === false && carIsValid){
this.AddedCars.push(car);
}
}
}
})
HTML:
<label for="carsId">Cars</label>
<select id="carsId" name="cars" v-model="SelectedCar">
<option disabled value="">Select</option>
<option v-for="car in DefaultCarList" :value="flavor">{{car}}</option>
</select>
<div>
<button type="button" class="hollow button success small"
v-on:click="addCar(SelectedCar)">Add Flavor</button>
</div>
Is it valid to iterate over an array like this in Vue and access the property by it's index? What is the correct way to do this?

Problem is with 'this' keyword it uses inner this where it doesn't have DefaultCarList variable, should use () => {} syntax .Error in this code
var carIsValid = function() {
for(var i = 0; i < defaultCarCount; i++)
{
if(this.DefaultCarList[i] === this.SelectedCar) // error here
{
return true;
}
}
return false;
}
should be
var carIsValid = () => {
for(var i = 0; i < defaultCarCount; i++)
{
if(this.DefaultCarList[i] === this.SelectedCar) // error here
{
return true;
}
}
return false;
}
and
var containsCar = () => {
for (var i = 0; i < addedCarCount; i++)
{
if (this.AddedCars[i] === car) // error here
{
return true;
}
}
return false;
}

The problem is that this it's not a reference to your model.
In your example this is a reference to window object.
Have a look here in order to understand the scope of this keyword in javascript.
You should use arrow functions.
var containsCar = () => {
for (var i = 0; i < addedCarCount; i++)
{
if (this.AddedCars[i] === car) // error here
{
return true;
}
}
return false;
}
or you could just define a self variable.
var self=this;
var containsCar = function() {
for (var i = 0; i < addedCarCount; i++)
{
if (self.AddedCars[i] === car) // error here
{
return true;
}
}
return false;
}
Further more, I recommand you to use native javascript functions in order to have a clean code.
var containsCar = function () {
for (var i = 0; i < addedCarCount; i++)
{
if (this.AddedCars[i] === car) // error here
{
return true;
}
}
return false;
}
var carIsValid = function() {
for(var i = 0; i < defaultCarCount; i++)
{
if(this.DefaultCarList[i] === this.SelectedCar) // error here
{
return true;
}
}
return false;
}
can be achieved using some method :
The some() method tests whether at-least one element in the array
passes the test implemented by the provided function.
var containsCar = () => {
return this.AddedCars.some(a=>a==car);
}
var carIsValid = () => {
return this.DefaultCarList.some(a=>a === this.SelectedCar);
}

JavaScript remove an IIFE event listener

I'm trying to remove click events from a list of id's after adding them with an IIFE like this
function setupPlayer(player){
var squareState = {};
for (i = 0; i < allSquares.length; i++) {
if(allSquares[i].innerHTML === "") {
// set up a click event for each square
document.getElementById(allSquares[i].getAttribute('id')).addEventListener('click', (clickSquare)(i));
}
}
}
The clickSquare function returns
function clickSquare(i){
var num = i;
return function() {
document.getElementById(allSquares[num].getAttribute('id')).innerHTML=player;
}
}
Then I try to remove them with
function removeClickEvents(){
for (let i = 0; i < allSquares.length; i++) {
document.getElementById(allSquares[i].getAttribute('id')).removeEventListener('click', clickSquare);
}
}
I've tried naming the returned anonymous function and using removeEventListener on that to no avail.

To remove event listener from a DOM element you need to pass the same function you used while adding event listener, as the parameter.
In javascript when you create an object it creates a new instance of that object class, so it won't be equal to another object even if it is created with same parameters
Example:
{} != {} // returns true
[] != [] // returns true
Same goes with function, whenever you write function (){} it creates a new instance of Function class.
Example:
function a() {
return function b() {}
}
a() != a() // returns true
Solution:
So for you to be able to remove the event listeners, you will have to store the functions you have passed to addEventListener
var listeners = [];
function setupPlayer(player) {
var squareState = {};
for (i = 0; i < allSquares.length; i++) {
if(allSquares[i].innerHTML === "") {
listeners[i] = clickSquare(i);
document.getElementById(allSquares[i].getAttribute('id')).addEventListener('click', listeners[i]);
}
}
}
function clickSquare(i) {
var num = i;
return function() {
document.getElementById(allSquares[num].getAttribute('id')).innerHTML=player;
}
}
function removeClickEvents() {
for (let i = 0; i < allSquares.length; i++) {
if(listeners[i]) {
document.getElementById(allSquares[i].getAttribute('id')).removeEventListener('click', listeners[i]);
}
}
}
From your code where you are using
document.getElementById(allSquares[i].getAttribute('id'))
I am assuming that allSquares[i] is a DOM element already, your code can be more simplified
var listeners = [];
function setupPlayer(player) {
var squareState = {};
for (i = 0; i < allSquares.length; i++) {
if(allSquares[i].innerHTML === "") {
listeners[i] = clickSquare(i);
allSquares[i].addEventListener('click', listeners[i]);
}
}
}
function clickSquare(i) {
var num = i;
return function() {
allSquares[num].innerHTML=player;
}
}
function removeClickEvents() {
for (let i = 0; i < allSquares.length; i++) {
if(listeners[i]) {
allSquares[i].removeEventListener('click', listeners[i]);
}
}
}

The function is being called immediately at (clickSquare)(i). At code at Question allSquares appears to be the element itself, clickSquare function can be referenced directly and event.target can be used within event handler to reference the current element in allSquares collection
let player = 123;
setInterval(() => player = Math.random(), 1000);
onload = () => {
let allSquares = document.querySelectorAll("div[id|=square]");
let button = document.querySelector("button");
button.onclick = removeClickEvents;
function setupPlayer(player) {
var squareState = {};
for (let i = 0; i < allSquares.length; i++) {
if (allSquares[i].innerHTML === "click") {
// set up a click event for each square
allSquares[i].addEventListener('click', clickSquare);
}
}
}
function clickSquare(event) {
console.log(event.target);
event.target.innerHTML = player;
}
function removeClickEvents() {
for (let i = 0; i < allSquares.length; i++) {
allSquares[i].removeEventListener('click', clickSquare);
}
}
setupPlayer(player);
}
<div id="square-0">click</div>
<div id="square-1">click</div>
<div id="square-2">click</div>
<button>remove events</button>

JavaScript: searching for a simple way of returning 'this' instead of 'val=x'

The following function returns val=ret instead of this. It is complicated and not clear:
getElement: function (nodeId) {
var ret = null;
if (nodeId === this._nodeId) {
ret = this;
} else {
for (var i = 0; i < this._selects.length; i++) {
ret = this._selects[i].getElement(nodeId);
if (ret) {
break;
}
}
}
return (ret);
},
Could you suggest an easier way for that? I tried the following, but you can't
do true/false with if(this._pages[i].getElement(nodeId):
getElement: function (nodeId) {
for (var i = 0; i < this._pages.length; i++) {
if(this._pages[i].getElement(nodeId){
return this;
}
}
return null;
},

I think you should return
this._pages[i].getElement(nodeId)

The second is not the same, because the first check is missing. (No need for an else part if a return is in the then part.)
getElement: function (nodeId) {
var i, ret;
if (nodeId === this._nodeId) {
return this;
}
for (i = 0; i < this._selects.length; i++) {
ret = this._selects[i].getElement(nodeId);
if (ret) {
return ret;
}
}
return null;
},

Repeat function in javascript

Could you please tell me how to make from this 4 functions just 1. Cause they all do one thing, with just one parameter changing all the time.
Also, I need to take the value of each time the function is running and put it into a new variable so I can after calculate it.
function getValue(age)
{
for (var i = 0; i < document.getElementsByName('age').length; i++)
{
if (document.getElementsByName('age')[i].checked)
{
return document.getElementsByName('age')[i].value;
}
}
}
function getBmiValue()
{
for (var i = 0; i < document.getElementsByName('bmi').length; i++)
{
if (document.getElementsByName('bmi')[i].checked)
{
return document.getElementsByName('bmi')[i].value;
}
}
}
function getFamValue()
{
for (var i = 0; i < document.getElementsByName('fam').length; i++)
{
if (document.getElementsByName('fam')[i].checked)
{
return document.getElementsByName('fam')[i].value;
}
}
}
function getDietValue()
{
for (var i = 0; i < document.getElementsByName('diet').length; i++)
{
if (document.getElementsByName('diet')[i].checked)
{
return document.getElementsByName('diet')[i].value;
}
}
}

function getValueByElementName(element_name)
{
for (var i = 0; i < document.getElementsByName(element_name).length; i++)
{
if (document.getElementsByName(element_name)[i].checked)
{
return document.getElementsByName(element_name)[i].value;
}
}
}
Or a little bit optimization:
function getValueByElementName(element_name)
{
var elements = document.getElementsByName(element_name);
for (var i = 0; i < elements.length; i++)
{
if (elements[i].checked)
return elements[i].value;
}
}

function getValue(tagname)
{
for (var i = 0; i < document.getElementsByName(tagname).length; i++)
{
if (document.getElementsByName(tagname)[i].checked)
{
return document.getElementsByName(tagname)[i].value;
}
}
}
Pass your element name as a variable in this function and call it.

Here is an example of what you can do:
function getValue(key) {
// get this once, not on each loop iteration
var elem = document.getElementsByName(key);
// cache the length too, so not to calculate it on each loop iteration
for (var i = 0, len = elem.length; i < len; i++) {
if (elem[i].checked) {
return elem[i].value;
// this will exit the function when it finds the FIRST one.
// Is that what you want?
}
}
}
// you can call above function like this:
getValue('age');
getValue('bmi');
getValue('fam');
getValue('diet');

JavaScript continue label scope

Map.prototype.updateMap = function (vehicles) {
nextVehicle:
for (var i = 0; i < vehicles.length; i++) {
for (var j = 0; j < this.oldVehicles.length; j++) {
var vehicle = vehicles[i];
var oldVehicle = this.oldVehicles[j];
if (vehicle.registration == oldVehicle.registration) {
oldVehicle.getPosition(function(latLng) {
if (vehicle.latitude != oldVehicle.lat) {
var newPos = new plugin.google.maps.LatLng(vehicle.latitude, vehicle.longitude);
oldVehicle.setPosition(newPos);
}
continue nextVehicle;
});
}
}
}
};
The code above does not work. I have a feeling this is to do with scope, I can't reach the nextVehicle label from inside the oldVehicle.getPosition method. How can I get around this?

Separate the matching logic from the update logic.
Map.prototype.updateMap = function (vehicles) {
// Only need to look up array lengths once
var vehiclesLength = vehicles.length,
oldVehiclesLength = this.oldVehicles.length;
for (var i = 0; i < vehiclesLength; i++) {
var vehicle = vehicles[i];
var oldVehicle = null;
// Find oldVehicle
for (var j = 0; j < oldVehiclesLength; j++) {
if (vehicle.registration == oldVehicle[j].registration) {
oldVehicle = oldVehicles[j];
break;
}
}
// Check for update if found
if (oldVehicle){
// Create closure for async callbacks
(function(oldV, lat,lng){
oldV.getPosition(function(latLng) {
if (lat != oldV.lat) {
var newPos = new plugin.google.maps.LatLng(lat,lng);
oldV.setPosition(newPos);
}
});
})(oldVehicle, vehicle.latitude, vehicle.longitude);
}
}
};

Just move the continue nextVehicle; line from inside the callback to immediately following the call to oldVehicle.getPosition(...):
Map.prototype.updateMap = function (vehicles) {
nextVehicle:
for (var i = 0; i < vehicles.length; i++) {
for (var j = 0; j < this.oldVehicles.length; j++) {
var vehicle = vehicles[i];
var oldVehicle = this.oldVehicles[j];
if (vehicle.registration == oldVehicle.registration) {
oldVehicle.getPosition(function(latLng) {
if (vehicle.latitude != oldVehicle.lat) {
var newPos = new plugin.google.maps.LatLng(vehicle.latitude, vehicle.longitude);
oldVehicle.setPosition(newPos);
}
});
continue nextVehicle;
}
}
}
};
This assumes the call to getPosition is a synchronous operation.
Edit:
Now if getPosition is asynchronous, you will need to use an asynchronous loop:
Something along this line might do the trick:
Map.prototype.updateMap = function (vehicles) {
var i = 0, j = -1, self = this;
var updatePosition = function() {
j++;
if (j == self.oldVehicles.length) {
j = 0;
i++;
}
if (i === vehicles.length) {
return; // We're done
}
var vehicle = vehicles[i];
var oldVehicle = self.oldVehicles[j];
if (vehicle.registration !== oldVehicle.registration) {
updatePosition();
}
else {
oldVehicle.getPosition(function(latLng) {
if (vehicle.latitude != oldVehicle.lat) {
var newPos = new plugin.google.maps.LatLng(vehicle.latitude, vehicle.longitude);
oldVehicle.setPosition(newPos);
updatePosition();
}
});
}
};
updatePosition();
};