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Array to Newline String to Array again through HTML

I have an array that comes in from from my API that I would like to arrange in a way that is better for the user (namely, in a column as opposed to the typical comma separated printed array).
This is my JS Fiddle to give a clearer picture: https://jsfiddle.net/2z89owas/
My question is, how can I get output3 to display just like output (and maintain its status as an iterable array like it was as dates)?

First you should not be using value for an html element. You can use .value for extracting value from inputs. Change your line to:
var val = document.getElementById('output2').innerHTML;
Afterwards, you have to split the same way you did join.
var dates3 = val.split('<br>');
document.getElementById('output3').innerHTML = dates3;

You can directly use join, something like:
document.getElementById('output3').innerHTML = dates.join(',');

You can try mapping over the contents of dates instead, as so:
let datesElem = dates.map(date =>`<p>${date}</p>`);
// test: console.log(datesElem)
document.getElementById('output3').innerHTML = datesElem

JS: encapsulated foreach loop with arrays for JSON

I'm trying to get a foreach loop in a second one.
My code:
var results = data.d.results;
var boxes= [
"Nmb1",
"Nmb2",
"Nmb3",
"Nmb4",
"Nmb5",
];
boxes.forEach(function(n){
var boxesEach = results[0].n.results;
boxesEach.forEach(function(i){
$("input[value="+'"'+i+'"'+"]").attr('checked', true);
});
});
What I'm trying to do is to make for example "Nmb1" replacing the "n" which would make the following "output code":
var boxesEach = results[0].Nmb1.results;
It works if I just put the code like that but not with the loop.
Thanks for help and tips.
BTW: I'm getting the JSON via AJAX from a Sharepoint 2013 server (with the REST API).

You need to use it like an index. This is called the bracket notation (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Property_Accessors#Bracket_notation)
var boxesEach = results[0][n].results;
The one you have right now tries to use a Dot notation for which you'd need the actual property name (i.e. Nmb1) and not a variable which holds the property name.

Read Value of JSON Result in Jquery

Here is my output of WebMethod through Ajax call:
var item=""[{\"Column1\":\"false\"}]""
There is always one row output,i-e true or false,i want to get the value of Column1,i already try Jquery.ParseJson(item),but it gives Illegal Token o error,Kindly help me how to read this value.Kindly check the inverted commas,this is the exact outcome of my web method, and this outcome and format is a necessary condition of scenario.Thanks.On using loop it gives the error:

If I understand your problem correctly, I think your extra quotes around the strings are a problem, this is invalid syntax.
This works:
var item = "[{\"Column1\":\"false\"}]";
var parsed = JSON.parse(item);
parsed.forEach(function(row) {
console.log(row.Column1);
});
console.log(parsed[0].Column1);
Here is a jsfiddle.
See here about jQuery.ParseJson vs JSON.parse, I prefer JSON.parse, but either should work fine.
In the case of older browsers without forEach use a for loop or a library like underscore.
var item="[{\"Column1\":\"false\"}]";
var parsed = JSON.parse(item);
//if forEach is not supported:
for (var i = 0; i < parsed.length; i++) {
console.log(parsed[i].Column1);
}
console.log(parsed[0].Column1);
Here is a for loop jsfiddle.

I understand that above solutions not work perfectly with your browsers, here is another alternate solution, though I know that it may not fit your scenario, but as your output is either true or false .Instead of using JsonConvert on server end, simply return the object array to client end and read value like this.
var tempo=item[0].Column1;

Not sure about the output of your service but I think you could try this:
str = 'var item=""[{\"Column1\":\"false\"}]""';
str = str.replace(/"/g, '');//remove quotes and slashes to make valid json
eval(str);//evaluate the string
console.log(item[0].Column1);

Why is my .data() function returning [ instead of the first value of my array?

I want to pass an array into a jQuery data attribute on the server side and then retrieve it like so:
var stuff = $('div').data('stuff');
alert(stuff[0]);
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.6.1/jquery.min.js"></script>
<div data-stuff="['a','b','c']"></div>
Why does this appear to alert '[' and not 'a' (see JSFiddle link)
JSFiddle Link: http://jsfiddle.net/ktw4v/3/

It's treating your variable as a string, the zeroth element of which is [.
This is happening because your string is not valid JSON, which should use double-quotes as a string delimiter instead of single quotes. You'll then have to use single-quotes to delimit the entire attribute value.
If you fix your quotation marks your original code works (see http://jsfiddle.net/ktw4v/12/)
<div data-stuff='["a","b","c"]'> </div>
var stuff = $('div').data('stuff');
When jQuery sees valid JSON in a data attribute it will automatically unpack it for you.

Declaring it as an attribute means that it is a string.
So stuff[0] would be equivalent to: var myString = "['a','b','c']"; alert(myString[0]);
You need to make it look like this:
<div data-stuff="a,b,c"></div>
var stuff = $('div').data('stuff').split(',');
alert(stuff[0]);
Retraction: jQuery's parsing fails because it didn't meet the rules of parseJSON.
However, I will stand behind my solution. There are aspects of the others that are less than ideal, just as this solution is less than ideal in some ways. All depends on what your paradigms are.

As others have identified the value is treated as string so it is returning "[". Please try this (aaa is the name of the div and I took out the data-stuff):
$(function(){
$.data($("#aaa")[0],"stuff",{"aa":['a','b','c']});
var stuff = $.data($("#aaa")[0],"stuff").aa;
alert(stuff[0]); //returns "a"
});

A different approach is posted at jsfiddle; var stuff = $('div').data('stuff'); stuff is a string with 0th character as '['
Well, var stuff = eval($('div').data('stuff')); should get you an array

getting variable/object elements and values in javascript

I'm not sure if I'm using the correct terminology, so please correct me if I'm not.
I've got a javascript variable which holds a group of values like this
var my_variables = {
first_var: 'starting',
second_var: 2,
third_var: 'continue',
forth_var: 'end'
}
Now I'm trying to get these variables in my script, but I don't want to have to check for each one.
Right now i'm doing this
if(my_variables.first_var!=null){
query=query+'&first_var='+my_variables.first_var;
}
if(my_variables.second_var!=null){
query=query+'&second_var='+my_variables.second_var;
}...
I'm hoping there is a simple way to recursively go through the object, but I haven't been able to find how to do that.
Something like
foreach(my_variables.??? as varName){
query=query+'&'+varName+'='+my_variables.varName;
}

Try this:
for(var key in my_variables)
query += '&'+key+'='+encodeURIComponent(my_variables[key]);

for (var varName in my_variables) {
query=query+'&'+varName+'='+my_variables[varName];
}
for (... in ...) is how you write this kind of loop in Javascript. Also use square brackets instead of a period when the field name is a value instead of the actual identifier, like here. Incidentally, I'd also suggest using window.encodeURIComponent if your values might contain arbitrary text.