Develop Reference

How can I convert the string value of a jQuery object into an actual jQuery object?

I have this string in my JS code right now:
newWords = '$(p span.word[style="--' + paraIndex + 'word-index:undefined"], p span.whitespace[style="--' + paraIndex + 'word-index:undefined"])';
I want to convert this string into a jQuery object that I can use do identify those specific elements.
I also saw the eval() function. That looks like it does what I want it to, but is super unsafe/unsecure.
Does anyone know a safe way to do this?

The simplest solution is to remove $( and ) and pass the remaining string as an argument to $():
var paraIndex = 0;
var newWords = '$(p span.word[style="--' + paraIndex
+ 'word-index:undefined"], p span.whitespace[style="--'
+ paraIndex + 'word-index:undefined"])';
var jQ = $(newWords.slice(2, -1));
console.log(jQ);
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

Pure Javascript - Turn number into a %

My program spits out a number between 0 and 1, and I cant change that. I need to turn it into a % to use as a variable for a CSS selector.
<div id="Value">0.50</div>
<script>
var element = document.getElementById("Value");
var percent = element * 100;
</script>
But how am I meant to put a % symbol on the end so I can do this:
document.getElementById("circle").style.marginLeft = percent;
Any help would be appreciated, thank you.

String concatenation:
document.getElementById("circle").style.marginLeft = percent + "%";
Since "%" is a string, percent will get converted to string and then the result will be the percent value followed by "%".
As Federico pointed out, you should be using either .value (if the id="Value" element is a field element [an input, textarea, or select]) or .textContent or .innerHTML (if it's not). In your case, it's a div, so textContent would make sense:
var value = document.getElementById("Value").textContent;
var percent = value * 100; // Implicitly converts `value` to number
document.getElementById("circle").style.marginLeft = percent + "%"; // Implicitly converts `percent` to string

try
circle.style.marginLeft = Value.innerText*100 + '%'
<div id="Value">0.50</div>
<div id="circle">◉<div>

document.getElementById("circle").style.marginLeft = percent + '%';
When used on strings, the + operator is called the concatenation operator.
Reference: Javascript Operators

This should solve it.
document.getElementById("circle").style.marginLeft = percent+"%";
In Javascript you can concat natively an int and a string using the '+' operator which means that -
var a = 5
var b = a + '%'
result is b = '5%'

Use innerHTML to get the text from the element
var element = document.getElementById("Value").innerHTML;
var percent = parseFloat(element)*100;
percent+='%';
console.log(percent)
<div id="Value">0.50</div>

Using the ".value" property of a textbox in Javascript

document.getElementById("t3").value = document.getElementById("t1").value +
document.getElementById("t2");
Through above code I could not get the result of addition of two numbers.

If you want to add those to values, you have to convert them to integer at first. .value always holds a string.
parseInt(document.getElementById("t1").value, 10) + parseInt(document.getElementById("t2").value, 10);

You are not actually adding two numbers together. You are attempting to add document.getElementById("t1").value (which is a string containing with numbers in it) to document.getElementById("t2"), which is a DOM element.
You probably get a result like this:
43[object HTMLInputElement]
You need to (a) get the value property of the second element and (b) add them together as numbers, rather than as strings.
document.getElementById("t3").value = (+document.getElementById("t1").value) +
(+document.getElementById("t2").value);
(+document.getElementById("t1").value) converts the value into a number. It is the unary plus + operator.

Try this:
document.getElementById("t3").value = parseInt(document.getElementById("t1").value,10) +
parseInt(document.getElementById("t2").value,10);

This is cheeky, but on the off-chance the t3 element that the OP is trying to update is a div or span rather than an input :)
var t1, t2, t3;
t1 = document.getElementById("t1");
t2 = document.getElementById("t2");
t3 = document.getElementById("t3");
t3.innerHTML = parseInt(t1.value, 10) + parseInt(t2.value, 10);
Or
t3.innerHTML = +t1.value + +t2.value;

How to add one to a variable to make 2 not 11

Currently this makes 11. It's for a slideshow and the var "n" equals 1 by default
function forward() {
document.getElementsByClassName("img")[0].setAttribute("class","imgout");
setTimeout( function() {
var n1 = document.getElementById("img").getAttribute("data-number");
var n=n1+1;
document.getElementById("img").setAttribute("data-number", n);
document.getElementById("img").setAttribute("src", "images/" + n + ".jpg");
document.getElementsByClassName("imgout")[0].setAttribute("class","img");
}, 500)
}

Use parseInt():
var n = parseInt(n1, 10) + 1;

Instead of:
var n=n1+1;
When n1 will be a string, because it came from the DOM, you need to convert n1 to an integer. There are many ways to do this, and really you should probably use a regular expression to validate that n1 contains what you expect first, but that being said you can try any of the following:
var n=parseInt(n1, 10)+1;
var n=(n1*1)+1;
var n=(+n1)+1;
As an aside the regex for validating the input from the DOM might be something such as:
/^-?\d+$/

Use Number():
var n = Number("1");
FIDDLE

parseInt - good choice. Also you can do
var n = n-0+1
Just remember that of you have different types "+" will convert to string and "-" will convert to numbers

Convert n1 to number as it is a string like ~~n1. The ~~n1 form is good if you know you want an integer (a 32-bit integer).
Second way is to use Number() function i.e. Number(n1) will convert n1 value into a string.

var n=parseInt(n)+1;
Documentation
Fiddle

JavaScript Calculation Problem - NaN message

I'm calculating a total number. I get the sum values from div's. But in total, instead of numbers I get (NaN - Not a Number)
JavaScript Function:
<script type="text/javascript">
function calculateTotal(){
var total = document.getElementById('valor1').innerHTML*1 + document.getElementById('valor2').innerHTML*1 + document.getElementById('valor3').innerHTML*1 + document.getElementById('valor4').innerHTML*1 + document.getElementById('valor5').innerHTML*1 + document.getElementById('valor6').innerHTML*1;
document.getElementById('total').innerHTML = total;
}
</script>
EDIT:
I found the error, I had a closing tag inside the DIV's like this:
<center><div id="valor1"></center></div>
Changed to:
<center><div id="valor1"></div></center>

You cannot use document.getElementById('valor1').innerHTML directly. You have to convert this to number. Please try this.
var value = document.getElementById('valor1').innerHTML;
var number = parseFloat(value)||0;
Do this for each div innerHTML which have number.
var number = parseFloat(value)||0;
The above line will help you to assign 0 to value if div is empty or div html cannot be converted to a number.

Use parseFloat(document.getElementById('x').innerHTML) to convert them to numbers before performing operations:
var total = parseFloat(document.getElementById('x1').innerHTML) + parseFloat(document.getElementById('x2').innerHTML);
You also may want to check them if they're numeric, here's a simple test using isNaN:
alert((isNaN("23"))?'not number':'number');

HTML:
<div id="valor1">2</div>
<div id="valor2">2</div>
<div id="valor3">ccccc</div>
<div id="valor4">2</div>
<div id="valor5">2</div>
<div id="valor6">2</div>
<hr/>
<div id="total">0</div>
JavaScript:
function $(id) { return document.getElementById(id); }
function get(elem) { return parseFloat($(elem).innerHTML) || 0; }
(function() {
var total =
get('valor1') * 1 + get('valor2') * 1 + get('valor3') * 1 +
get('valor4') * 1 + get('valor5') * 1 + get('valor6') * 1;
$('total').innerHTML = total;
}());
A little optimization of the work and demo.
But why stop here? :) we can make it even better ( I think ):
function get(elem) {
return (parseFloat($(elem).innerHTML) || (function() {
$(elem).innerHTML += " <i>Not a number assumed 0</i>";
return 0;
}()));
}
And the updated demo.
Edit: no errors on Chrome & Mozilla (Linux).

try using parseInt() as in
var total = parseInt(document.getElementById('valor1').innerHTML)*1 + parseInt(document.getElementById('valor2').innerHTML)*1 + ... ;
etc etc
this will ensure that what you're getting out of the fields is in fact, a number

Did you try to put these parts into brackets?
(document.getElementById('valor1').innerHTML * 1) + ...
See: http://rx4ajax-jscore.com/ecmacore/operator/predence.html
Even better - use the parseInt(var string) function;
parseInt(document.getElementById('valor1').innerHTML) + ...