Develop Reference

createElement creates infinite loop

I'm really new to javascript, and coding in general, and I can't understand why this causes an infinite loop:
let newTr = document.createElement('tr');
If I take it out, the webpage loads fine, but if I leave it in, the webpage never fully loads and my browser uses 50% of my CPU.
Here's the rest of my code:
// client-side js
// run by the browser each time your view template referencing it is loaded
console.log('hello world :o');
let arrPfcCases = [];
// define variables that reference elements on our page
const tablePfcCases = document.getElementById("tablePfcCases");
const formNewPfcCase = document.forms[0];
const caseTitle = formNewPfcCase.elements['caseTitle'];
const caseMOI = formNewPfcCase.elements['caseMOI'];
const caseInjuries = formNewPfcCase.elements['caseInjuries'];
// a helper function to call when our request for case is done
const getPfcCaseListener = function() {
// parse our response to convert to JSON
arrPfcCases = JSON.parse(this.responseText);
// iterate through every case and add it to our page
for (var i = 0; i = arrPfcCases.length-1;i++) {
appendNewCase(arrPfcCases[i]);
};
}
// request the dreams from our app's sqlite database
const pfcCaseRequest = new XMLHttpRequest();
pfcCaseRequest.onload = getPfcCaseListener;
pfcCaseRequest.open('get', '/getDreams');
pfcCaseRequest.send();
// a helper function that creates a list item for a given dream
const appendNewCase = function(pfcCase) {
if (pfcCase != null) {
tablePfcCases.insertRow();
let newTr = document.createElement('tr');
for (var i = 0; i = pfcCase.length - 1; i++) {
let newTd = document.createElement('td');
let newText = document.createTextNode(i.value);
console.log(i.value);
newTd.appendChild(newText);
newTr.appendChild(newTd);
}
tablePfcCases.appendChild(newTr);
}
}
// listen for the form to be submitted and add a new dream when it is
formNewPfcCase.onsubmit = function(event) {
// stop our form submission from refreshing the page
event.preventDefault();
let newPfcCase = [caseTitle, caseMOI, caseInjuries];
// get dream value and add it to the list
arrPfcCases.push(newPfcCase);
appendNewCase(newPfcCase);
// reset form
formNewPfcCase.reset;
};
Thanks!
P.S. There are probably a ton of other things wrong with the code, I just can't do anything else until I figure this out!

As an explanation, in your code
i = pfcCase.length - 1
assigned the value of pfcCase.length - 1 to i. The syntax of that part of the loop should be
an expression to be evaluated before each loop iteration. If this expression evaluates to true, statement is executed.
The evaluation of your code made no sense.
Evaluating
i < pfCase.length
before each iteration to check that the current index is less than the length of the array, however, works correctly.

Here is no conditional statement here. In this statement you are assigning pfcCase length minus 1 to the I variable.
for (var i = 0; i = pfcCase.length - 1; i++) {
You have to compare the i variable to the length of the pfcCase minus 1.
This should work.
for (var i = 0; i < pfcCase.length - 1; i++) {
noticed something else
This line does not do what you think it dose.
let newText = document.createTextNode(i.value);
i is just the index i.e. a number. It does not have the value property.
This is what you are looking to do.
let newText = document.createTextNode(pfcCase[i].value);
my preference (forEach)
I prefer using the array forEach method. It’s cleaner and less prone to mistakes.
pfcCase.forEach( function(val){
let newTd = document.createElement('td');
let newText = document.createTextNode(val.value);
console.log('The array element is. '. val.value, ' The value is. ', val.value);
newTd.appendChild(newText);
newTr.appendChild(newTd);
});

Updating the value of an object inside a loop using javascript

I'm currently facing a difficulty in my codes.
First i have an array of objects like this [{Id:1, Name:"AML", allowedToView:"1,2"}, {Id:2, Name:"Res", allowedToView:"1"}...] which came from my service
I assign it in variable $scope.listofResource
Then inside of one of my objects I have that allowedToView key which is a collection of Id's of users that I separate by comma.
Then I have this code...
Javascript
$scope.listofResource = msg.data
for (var i = 0; i < msg.data.length; i++) {
First I run a for loop so I can separate the Id's of every user in allowedToView key
var allowed = msg.data[i].allowedToView.split(",");
var x = [];
Then I create a variable x so I can push a new object to it with a keys of allowedId that basically the Id of the users and resId which is the Id of the resource
for (var a = 0; a < allowed.length; a++) {
x.push({ allowedId: allowed[a], resId: msg.data[i].Id });
}
Then I put it in Promise.all because I have to get the Name of that "allowed users" base on their Id's using a service
Promise.all(x.map(function (prop) {
var d = {
allowedId: parseInt(prop.allowedId)
}
return ResourceService.getAllowedUsers(d).then(function (msg1) {
msg1.data[0].resId = prop.resId;
Here it returns the Id and Name of the allowed user. I have to insert the resId so it can pass to the return object and it will be displayed in .then() below
return msg1.data[0]
});
})).then(function (result) {
I got the result that I want but here is now my problem
angular.forEach(result, function (val) {
angular.forEach($scope.listofResource, function (vv) {
vv.allowedToView1 = [];
if (val.resId === vv.Id) {
vv.allowedToView1.push(val);
I want to update $scope.listofResource.allowedToView1 which should hold an array of objects and it is basically the info of the allowed users. But whenever I push a value here vv.allowedToView1.push(val); It always updates the last object of the array.
}
})
})
});
}
So the result of my code is always like this
[{Id:1, Name:"AML", allowedToView:"1,2", allowedToView:[]}, {Id:2, Name:"Res", allowedToView:"1", allowedToView:[{Id:1, Name:" John Doe"}]}...]
The first result is always blank. Can anyone help me?
Here is the plunker of it... Plunkr

Link to the solution - Plunkr
for (var i = 0; i < msg.length; i++) {
var allowed = msg[i].allowedToView.split(",");
msg[i].allowedToView1 = [];
var x = [];
Like Aleksey Solovey correctly pointed out, the initialization of the allowedToView1 array is happening at the wrong place. It should be shifted to a place where it is called once for the msg. I've shifted it to after allowedToView.split in the first loop as that seemed a appropriate location to initialize it.

TypeError: 'undefined' is not an object in Javascript

I have a piece of Javascript code that assigns string of values to a string array.
Unfortunately if I try to add more than one string to the array, my UI simulator(which runs on JS code) closes unexpectedly. I have tried debugging but I cannot find anything. I am attaching that piece of code where the issue is. may be you guys could find some flaw? On the pop up button click the values I selcted on the UI should get stored in the array and I have a corressponding variable on the server side to handle this string array.
_popupButtonClick: function (button) {
var solutions = this._stateModel.get('solutionName');
var i;
var solutionsLength = solutions.length;
var selectedSolution = [solutionsLength];
this.clearPopupTimer();
if (button.position === StatusViewModel.ResponseType.Ok) {
for(i=0;i<solutionsLength;i++)
{
if(this._list.listItems[i].selected)
{
selectedSolution[i] = this._list.listItems[i].options.value;
}
}
this._stateModel.save({
selectedsolutions: selectedSolution,
viewResponse: StatusViewModel.ResponseType.Ok
});
} else {
this._stateModel.save({
viewResponse: StatusViewModel.ResponseType.Cancel
});
}
}

Change
var selectedSolution = [solutionsLength];
to
var selectedSolution = [];
This makes your array have an extra item that might be causing a crash.
Also,
you have an
if(this._list.listItems[i].selected)
{
selectedSolution[i] = this._list.listItems[i].options.value;
}
But no corresponding else, so your array has undefined values for i which are not entering the if.
Maybe adding an empty string might solve it:
if(this._list.listItems[i].selected)
{
selectedSolution[i] = this._list.listItems[i].options.value;
}
else
{
selectedSolution[i] = "";
}

The code is looking fine but there seems to be a piece of code which can cause error. For example, you are assigning var selectedSolution = [solutionsLength]; and for example solutionsLength is 5 then your loop runs for 5 times
for(i=0;i<solutionsLength;i++) // runs for 5 times
{
if(this._list.listItems[i].selected)
{
// but selectedSolution = [5]; which is on 0th index and from 1st to 4th index it is undefined
selectedSolution[i] = this._list.listItems[i].options.value;
}
}
So you can try to use push() like
selectedSolution.push(this._list.listItems[i].options.value);
and on initialization change it like,
var selectedSolution = [];
Hopefully this will solve your problem.

var selectedSolution = [solutionsLength];
keeps the value in the selectedSolution variable.
var selectedSolution = [3];
selectedSolution[0] gives the values as 3
So make it simple
var selectedSolution = [];

Javascript for loop function array

I'm bit of a javascript newbie - I'm trying to make a function that when I click a button it will call out a single object out of my array, in order.

all it does is display "ee".
Of course, you are looping through the whole array and assigning each item to the innerHTML of that one element - and only the last one will stay there and show up.
What I want it to do is when I click the button to display "aa" then when I press it again to display "bb" instead of "aa" and so on.
Then you can't use a for-loop, but have to keep track of the counter manually and execute only one step per invocation of call.
var myArray = ["aa","bb","cc","dd","ee"];
var i=0;
function call() {
document.getElementById("placeDiv").innerHTML = myArray[i];
if (i < myArray.length-1)
i++;
else
i = 0; // restart, but you may as well show an error message
}

You want a closure.
var call = (function() {
var i = 0,
entries = ["aa", "bb", "cc", "dd", "ee"];
return function() {
return entries[i++ % entries.length];
};
})();
This keeps i and entries as private values, and returns a function that goes to the next entry in the list each time it is called.

Try this:-
You are looping through on each click and assigning value to the element innerHTML so it will always have only the last value from the array.
Demo
var myArray = ["aa","bb","cc","dd","ee"];
var i = 0;
function call(){
if(myArray.length <= i) i=0;
document.getElementById("placeDiv").innerHTML = myArray[i++];
}
if you don't want to use a global variable you can use this way too.
http://jsfiddle.net/zZ4Rm/
Use shift method on array to get the first item and then push it back tht end of the array for the cycle to happen.
var myArray = ["aa","bb","cc","dd","ee"];
function call(){
var val = myArray.shift();
myArray.push(val);
document.getElementById("placeDiv").innerHTML = val;
}

You are overwritting your placeDiv with innerHTML.
Try using:
function call(){
var yourVar= document.getElementById('placeDiv');
for (var i=0; i < myArray.length; i++) {
yourVar.innerHTML = yourVar.innerHTML + myArray[i];
}
}

<script type="text/javascript">
var myArray = ["aa","bb","cc","dd","ee"],
num=0;
function call() {
document.getElementById("placeDiv").innerHTML = myArray[num];
num++;
};
</script>
<button onclick="call()">Click!</button>
<div id = "placeDiv"></div>

JavaScript stop referencing object after pass it to a function

I know JavaScript passes Objects by reference and thus I'm having a lot of trouble with the following code:
function doGradeAssignmentContent(dtos) {
var x = 5;
var allPages = [];
var stage = new App.UI.PopUpDisplay.PopUpStageAssignmentGrader(null, that);// pass launch element
for(var i = 0; i < dtos[0].result.students.length; ++i) {
var pagesSet = [];
for(var j = 0; j < dtos[0].result.questions.length; ++j) {
var questionObject = jQuery.extend(true, {}, new Object());
questionObject = dtos[0].result.questions[j];
if(dtos[0].result.students[i].answers[j].assignmentQuestionId === questionObject.questionId) {// expected, if not here something is wrong
questionObject.answer = dtos[0].result.students[i].answers[j].studentAnswer;
questionObject.pointsReceived = dtos[0].result.students[i].answers[j].pointsReceived;
} else {
var theAnswer = findAssociatedStudentAnswer(questionObject.questionId, dtos[0].result.students[i].answers[j]);
if(theAnswer !== null) {
questionObject.answer = theAnswer.studentAnswer;
questionObject.pointsReceived = theAnswer.pointsReceived;
} else {
alert("Unexpected error. Please refresh and try again.");
}
}
pagesSet[pagesSet.length] = new App.UI.PopUpDisplay.StageAssignmentGradingPages[dtos[0].result.questions[j].questionType.charAt(0).toUpperCase() + dtos[0].result.questions[j].questionType.slice(1) + "QuestionAssignmentGradingPage"](j + 1, questionObject);
}
var studentInfo = {};
studentInfo.avatar = dtos[0].result.students[i].avatar;
studentInfo.displayName = dtos[0].result.students[i].displayName;
stage.addPageSet(pagesSet, studentInfo);
}
stage.launch();
}
First let me show you what the result (dtos) looks like so you can better understand how this function is parsing it:
The result (dtos) is an Object and looks something like:
dtos Array
dtos[0], static always here
dtos[0].result, static always here
dtos[0].questions Array
dtos[0].questions.index0 - indexN. This describes our Questions, each one is an Object
dtos[0].students Array
dtos[0].students[0]-[n].answers Array. Each student array/Object has an Answers array. Each student will have as many elements in this answers Array that there were questions in dtos[0].questions. Each element is an Object
Now what we do in this here is create this Object stage. Important things here are it has an array called "this.studentsPages". This array will ultimately have as many entries as there were students in dtos[0].students.
So we loop through this for loop disecting the dtos array and creating a pagesSet array. Here comes my problem. On the first iteration through the for loop I create this questionObject element. I also have tried just doing var questionObject = {}, but what you see now was just an attempt to fix the problem I was seeing, but it didn't work either.
So at the end of the first iteration of the outer for loop I call stage.addPageSet, this is what happens here:
var pageObject = [];
pageObject["questions"] = pageSet;
pageObject["displayName"] = studentInfo.displayName;
this.studentsPages[this.studentsPages.length] = pageObject;
if(this.studentsPages.length === 1) {// first time only
for(var i = 0; i < pageSet.length; ++i) {
this.addPage(pageSet[i]);
}
}
The important thing to take notice of here is where I add pageObject on to this.studentsPages which was an empty array before the first call. pageObject now has pageSet plus a little bit more information. Remember, pageSet was an Object and thus passed by reference.
On the next iteration of the for loop, when I hit this line:
questionObject.answer = dtos[0].result.students[i].answers[j].studentAnswer;
It goes wrong. This changes the local copy of questionObject, BUT it also changes the copy of questionObjec that was passed to addPageSet and added to the studentsPages array in the first iteration. So, if I only had 2 students coming in, then when all is said and done, studentsPages hold 2 identical Objects. This should not be true.
The problem is questionObject in the doGradeAssignmentContent function is keeping a reference to the Object created on the previous iteration and then overrides it on all subsequent iterations.
What can I do to fix this?
Thanks for the help!

With out having looked at it too closely I believe you need to change the following:
// Before:
var questionObject = jQuery.extend(true, {}, new Object());
questionObject = dtos[0].result.questions[j];
// After:
var questionObject = jQuery.extend(true, {}, dtos[0].result.questions[j]);
I didn't look too closely if there are other instances in the code where this needs to be applied, but the core concept is to utilize jQuery's deep copy to generate a duplicate of the object you do not wish to retain a reference to.