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How do i push an array[i] to another array

Basically i have to create a quiz with 3category. each with 5questions.
I would have to push the selected category-questions into this new array from the array with all the questions. I am unable to do so.
pushSelectedQuestion() {
for (var i = 0; i < this.getNumberOfQuestion; i++) {
if (usercategory == questionPool[i].category) {
mcqSelected.push(questionPool[i])
return mcqSelected;
}
}
}
usercategory = input from user.
if user chooses category 1.
if (1 == questionPool[1].category) (if it matches the category) then it will be pushed.
This is the part which i cant do

Well, from the information you've provided, there's one main issue here - the return statement is definitely shortcutting the loop - so even if you have everything else right, you'll only ever get the first matching question. The rest will have been cut out by the return statement, which stops the function and returns the value.
pushSelectedQuestion() {
for (var i = 0; i < this.getNumberOfQuestion; i++) {
if (usercategory == questionPool[i].category) {
mcqSelected.push(questionPool[i])
// the below line is causing this loop to end after the first time through the list.
// Remove it and then put a console.log(mcqSelected);
// here instead to see the value during each iteration of the loop.
return mcqSelected;
}
}
}
There are a lot of ways to accomplish what you want to do here though. For example, you could just use the javascript Array.filter method like so
let selectedQuestions = questionPool.filter(question => question.category == userCategory)

Maybe I am not understanding your question correctly, but can't you use nested arrays. If the questions are categorized beforehand that is.

localStorage array is being overwritten after refresh

So my localStorage values in array are being overwritten after the refresh. While in session, I can change values on front end and array in localStorage constantly will be updated or if more inputs changed, then more values to array added. If for example I had 3 inputs changed and all their values was added to localStorage array in the session then after webpage refresh if I will edit one of the inputs again, all the arrays in localStorage will be deleted and overwritten by the new's session update of input. I'm trying to figure out this for a long time, but can't figure out how to make it work so that after the refresh all the input values would be stored in the old array and not overwritten.
var presetsArr = [];
if (!localStorage.getItem("presetsArr") || localStorage.getItem("presetsArr").length < 0) {
init();
} else {
initIfLocalStorage();
}
function initIfLocalStorage () {
presetsArr = JSON.parse(localStorage.getItem('presetsArr'));
for (var i = 0; i < presetsArr.length; i++) {
if (presetsArr[i].freq) {
osc.frequency.value = presetsArr[i].freq;
freqSlider.value = presetsArr[i].freq;
freqDisplay.innerHTML = freqSlider.value;
}
if (presetsArr[i].detune) {
osc.detune.value = presetsArr[i].detune;
detuneSlider.value = presetsArr[i].detune;
detuneDisplay.innerHTML = detuneSlider.value;
}
if (presetsArr[i].gain) {
volume.gain.value = presetsArr[i].gain;
}
}
freqSlider.addEventListener("click", function(e) {
osc.frequency.value = this.value;
freqDisplay.innerHTML = this.value;
bookmark["freq"] = osc.frequency.value;
presetsArr.push(bookmark);
presetsArr = localStorage.setItem("presetsArr", JSON.stringify(presetsArr)) || [];
})
detuneSlider.addEventListener("click", function(e) {
osc.detune.value = this.value;
detune.innerHTML = this.value;
bookmark["detune"] = osc.detune.value;
presetsArr.push(bookmark);
presetsArr = localStorage.setItem("presetsArr", JSON.stringify(presetsArr)) || [];
})
Here is what I mean: First session, I changed both frequency and detune values, they got stored in the array. http://imgur.com/0GIeQPj
Now after refresh in the second session, I changed the detune value again and the whole localStorage array got overwritten. Now frequency key is gone and only detune left. So after refresh next time I want to play my oscillator, I won't get any sound out of it, because frequency value in the array was removed.
http://imgur.com/crTywnN

For anyone running in the same kind of problem, here is the solution I came across.
So like Patrick Evans said, I made a mistake by assigning .setItem() to a variable, even though .setItem() doesn't return any value. So I just always create a new empty array when I click after the resfresh (in the new session). But that is not enough. Now I was running into a problem, where I was trying to push values into non-existing array and getting null error. I changed my click handler to:
presetsArr = JSON.parse(localStorage.getItem('presetsArr')) || [];
presetsArr.push(bookmark);
localStorage.setItem("presetsArr", JSON.stringify(presetsArr));
|| [] helped me to get rid of Null error. Even though I created en empty array at the top of my program, for some reason inside the click hander I couldn't push anything to it, so this little shortcut helped me to check if there is an array to push to and if there is not, then create one before pushing.
Now I can refresh the webpage and continue changing input values without overwriting and recreating localStorage array.

JS multidimensional array spacefield

i wanna generate a 3x3 field. I want to do this with JS, it shall be a web application.
All fields shall inital with false. But it seems so that my code is not working correctly, but i don't find my fault. The goal is, that every spacesector is accessible.
Thats my idea:
// define size
var esize = generateSpace(3);
}

space[i] = false is replacing the array with a single boolean value false, not filling in all the entries in array you just created. You need another loop to initialize all the elements of the array.
function generateSpace(x) {
var space = [];
for (var i = 0; i < x; i++) {
space[i] = [];
for (var j = 0; j < x; j++) {
space[i][j] = false;
}
}
return space;
}
Also, your for() loop condition was wrong, as you weren't initializing the last element of space. It should have been i < space.length.
And when it's done, it needs to return the array that it created.

Since I got somewhat bored and felt like messing around, you can also initialize your dataset as shown below:
function generateSpace(x) {
return Array.apply(null, Array(x)).map(function() {
return Array.apply(null, Array(x)).map(function() {
return false;
});
});
}

The other functions work equally well, but here's a fairly simply looking one using ES6 that works for any square grid:
function generateSpace(x) {
return Array(x).fill(Array(x).fill(false));
}

Passing array of objects to a js function

i am trying for the first time to implement OOP in javascript and i got stuck on a recursive function when i try to send an array of objects to this function. So, i have the "Pitic" class (pitic means midget in romanian) with some propreties:
function Pitic(piticID) {
this.id = piticID;
this.inaltime = null;
this.greutate = null;
this.genereazaGreutate();
this.genereazaInaltime();
}
I'm now generating some midgets and storing them in the public piticiCollection Array variable. The "genereazaGreutate" and "genereazaInaltime" are function to generate random values for the inaltime and greutate values.
var pitic = new Pitic(idPitic);
piticiCollection.push(pitic);
The problem appears when i try to send the array of midgets to a function because all i get is only the first item of the array.
So, before i call the function, i have piticiCollection array with 4 objects:
midgets are safe and sound http://img443.imageshack.us/img443/484/yr4f.png
And as soon as i call the function with the piticiCollection as a parameter i loose 3 midgets! :(
most of the midgets are gone http://img201.imageshack.us/img201/5808/7od5.png
p.s. please excuse me for my bad english..
[EDIT]
Here is a fiddle of my full code: http://jsfiddle.net/WT7Ud/ I call the function on line 56 and as soon as the debugger hits line 60 i loose array items.

I have solved my problem by creating a copy of the array before using it in the function. Strange :(
function determinaPerechi(somePitici) {
var piticDeComparat, colectieDePiticiCopy;
colectieDePiticiCopy = somePitici;
for (var i = 1; i < colectieDePiticiCopy.length; i++) {
var piticDeComparat2 = null;
piticDeComparat = colectieDePiticiCopy[0];
piticDeComparat2 = colectieDePiticiCopy[i];
if (piticDeComparat.inaltime < piticDeComparat2.inaltime) {
//Perechea poate fi prietena
}
}
//colectieDePiticiCopy.splice(0, 1);
if (colectieDePiticiCopy.length == 0) {
//alert("finish");
return;
}
determinaPerechi(colectieDePiticiCopy);
//test(ttt);
}

Your determinaPerechiPosibile is modifying the original array on this line:
colectieDePitici.splice(1, colectieDePitici.length);
In particular, it is removing all but the first element. You probably should be using slice to non-destructively extract the part of the array you want to recurse on.

As Ted Hopp mentioned, the problem appears to be the line
colectieDePitici.splice(1, colectieDePitici.length);
in combination with this line:
determinaPerechiPosibile(colectieDePiticiCopy);
If those two lines are commented out, the array maintains its original length.

For loop exiting early while updating modified or new records in datatable.net table

I'm using the Datatables jQuery plugin. The table is pulling the data from an AJAX source (a SQL Server query, processed by ASP.NET into a JSON object). I want to create a live view of the table so that changes appear in real time. But rather than reloading the entire table every few seconds with fnReloadAjax() (which, from experience, has proven to be quite burdensome on the browser) I'm only updating the records that are new or modified, using fnAddData() and fnUpdate().
After getting a JSON object of just the new or modified records, here's my code to process the object.
var newData = updatedDataJSON.aaData;
if (newData[0] != null) {
for (i = 0; i < newData.length; i++) { //Loop through each object
if (newData[i].bNewCase === true) { //Process new cases
oTable.fnAddData(newData[i]);
} else { //Process modified cases
var tableArray = oTable.fnGetData();
var index;
var found = false;
var serial = newData[i].serial;
var dataObject = newData[i];
//First gotta find the index in the main table for
// the record that has been modified. This is done
// by matching the serial number of the newData
// object to the original aData set:
for (ii = 0; ii < tableArray.length; ii++) {
var value = tableArray[ii]['serial'];
value = value.replace(/<\/?[^>]+(>|$)/g, "");
if (value === serial) {
index = ii;
found = true;
}
}
if (found) {
oTable.fnUpdate(dataObject, index);
console.log('Updated ' + newData[i].serial);
}
}
}
}
My problem is that even though the newData.length property of the first for loop could be greater than 1, the for loop exits early (after one iteration). I added the console.log statement at the end and it started passing errors saying that newData[i].serial was undefined. This makes me think that the entire newData array was destroyed or something...
I'm really hoping that I've just made a stupid mistake (though I've checked and checked and checked some more but can't find one). Maybe there's something that I'm overlooking. If anyone has any advice, it would be greatly appreciated.

Credit goes to #elclarnrs for the solution, posted above in the comments. The solution was declaring the values of i and ii in the scope of the function. That got everything working smoothly. Good to know for future reference.