Develop Reference

How to get an 8 decimal output?

I am trying to get an 8 decimal output from the following function.
The following function multiplies an input by 2 and then updates this input with the wagerUpdate variable. I would like this outputted number to have 8 decimal places.
For example: if input number is 0.00000001 (this code is for a bitcoin website), then I would like output number to be 0.00000002. For some reason the code below is not working properly as the output number is in the format of 2e-8 without the .toFixed(8) code. Please help if you are able to. Thank you so much.
<script>
function MultiplyWagerFunction() {
var wager = document.getElementById("wagerInputBox").value;
var wagerUpdate = wager*2;
document.getElementById("wagerInputBox").value = +wagerUpdate.toFixed(8);
}
</script>

If you remove the + before wagerUpdate.toFixed(8) it should work fine. wagerUpdate has already be converted to a number when you multiplied it by 2 so there should be no need for the unary +
var a = "0.00000001";
var b = a*2;
console.log(b.toFixed(8));
console.log(+b.toFixed(8));
^ see the difference.
The reason it doesn't work is because what you are doing is equivalent to:
+(b.toFixed(8))
because of the precedence of the operators (member access . is higher than unary +). You are converting b to a string with .toFixed and then converting it back into a number with + and then converting it back into a string again! (this time with the default toString behavior for numbers giving you exponential notation)

Just remove + from +wagerUpdate.toFixed(8); and you would be good.

Instead of:
document.getElementById("wagerInputBox").value = +wagerUpdate.toFixed(8);
try:
document.getElementById("wagerInputBox").innerHTML = +wagerUpdate.toFixed(8);
Why I say so is may be when you set value, browser tries to convert to best possible outcome. But, inner HTML should take the string equivalent!

Is using parseInt extraenous if unnecessary?

I am a beginner to coding and JavaScript but I am doing a practice exercise and I came across something I am unsure about.
var nameLength = parseInt(fullName.length);
var nameLength = fullName.length;
I used the first line not even thinking it would already be an integer, so should I still have included the parseInt or not?

Yes, remove var nameLength = parseInt(fullName.length); Below is your explanation:The parseInt() method in JavaScript is used to turn the integer value of a string into an integer. If I have string, say var s = "3";, I could use the + operator to it, but it wouldn't add as if they were numbers (ex. s += 9;, then s would equal "39"). You call the parseInt() method only if you have a value with the type of string. In your case, and in most, if not all languages, the .length or .length() of anything will return an integer. What you're doing is trying to convert a number to a number, which is (after I googled the definition) extraneous.

Javascript parseInt not working on a string, trying to get an integer from an HTML value

I am making a basic game, and I have a tile system that I'm using. Each tile has an ID of "tileX", where X is a number (ex. tile1). I have a function as follows:
window.onclick = function() {
var x = event.clientX, y = event.clientY,
elementMouseIsOver = document.elementFromPoint(x, y).id;
document.getElementById("tileTell").value = elementMouseIsOver;
console.log(elementMouseIsOver);
console.log(typeof(elementMouseIsOver));
elementMouseIsOver = parseInt(elementMouseIsOver);
console.log(elementMouseIsOver);
console.log(typeof(elementMouseIsOver));
}
Line 4 of code there fills in an input field so I can visually see which tile I've clicked (I'm using this to make sure things are working properly and so I can find the tiles I need). That works fine. On line 5 when I do a console.log, it gives me the proper ID, and verifies that it is a string.
After that I want to reset the elementMouseIsOver variable to be an integer, so if the ID was tile1 I would expect the new result to be 1. But when I look at it in the console, I get NaN. And then when I check the type of it immediately after that, I get number.
The parseInt does not seem to be working properly, what am I doing wrong? I need to use the ID names of each tile for mathematical operations so this is vital to my game. I know it's probably a really dumb mistake but I am completely at a loss...

If you want parseInt() to work on strings in the way you're using it, it has to start with a digit; in your case, it starts with alphabetical characters, and so (with an implicit radix of 10) it will rightfully return NaN.
You could get the number out by using a generic method:
var num = +(elementMouseIsOver.match(/\d+/) || [])[0];
It matches the first group of digits it can find and then uses the unary plus operator to cast it into an actual number value. If the string doesn't contain any digits, it will yield NaN.
In your particular case, you could also apply parseInt() on the part that immediately follows "tile":
var num = +elementMouseIsOver.substr(4);

NaN is correct.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt
If parseInt encounters a character that is not a numeral in the specified radix, it ignores it and all succeeding characters and returns the integer value parsed up to that point.
Nothing parsed successfully.
EDIT
You could accomplish what you want by removing the non-numeric characters from the string, assuming you'll always have a string+integer as the ID. Try this:
parseInt(elementMouseIsOver.replace(/[^\d]/,""))

You need to remove the "tile" string first, so it can properly parse the value:
elementMouseIsOver = parseInt(elementMouseIsOver.substring("tile".length));
.substring("tile".length) returns a substring starting with the character after "tile" (position 4 in the string, count starts at 0), resulting in only the number of the ID (as a string).
fiddle: http://jsfiddle.net/rk96uygd/

The typeof of a NaN is number.
Use isNaN() to test if a value is NaN or Not a Number
https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/isNaN
You could also use the Number() cast instead of parseInt().

you trying to parseInt on a element ID that is non-numeric, when parse fail it will return NaN (*or not a number*)
elementMouseIsOver = parseInt(elementMouseIsOver);
moreover, your elementMouseIsOver is an ID of control, I don't think .value can get the value of control
elementMouseIsOver = document.elementFromPoint(x, y).id;

How does join() work?

I was doing a JS quiz and stumbled uppon this question.
What does this function return?
function Batman()
{
return Array(4).join("lol" - 2) + " Batman!";
}
This actually happens to return NaNNaNNaN Batman! which i found rather funny.
But why does it return exactly this? i mean it stores NaN 3 times and suddenly it skips that and puts batman in the final index. While afaik the exact same thing happens for each array index.

I am not getting what you want to do.
Your function works like bellow.
Array(4) //retruns [undefined × 4]
You are saying
[undefined × 4].join("lol"-2)
Here because "lol"-2 returns NaN it will return "NaNNaNNaN"
And after this you are appendig the result to " Batman!" so the last result will be
"NaNNaNNaN Batman!"

The code tries to subtract 2 from "lol". But because "lol" isn't a number, the result isn't a number either; that gets represented internally by a value known as "Not a Number", or "NaN" for short.
You've got several of those in an array. When you try to join them all together as strings, and add on " Batman!" to the end, the NaN gets converted to its most sensible string representation, which is just NaN.
So you end up with several copies of "NaN", followed by "Batman!".
See Wikipedia's entry on NaN.

The expression Array(4).join("lol" - 2) returns a string consisting of 3 NaN. The + operator concatenates " Batman!" at the end of the previous string (it does not append any item to any array, since join() returns a string). So, the function returns that funny sentence.

What is the difference between Number(...) and parseFloat(...)

What is the difference between parseInt(string) and Number(string) in JavaScript has been asked previously.
But the answers basically focused on the radix and the ability of parseInt to take a string like "123htg" and turn it into 123.
What I am asking here is if there is any big difference between the returns of Number(...) and parseFloat(...) when you pass it an actual number string with no radix at all.

The internal workings are not that different, as #James Allardic already answered. There is a difference though. Using parseFloat, a (trimmed) string starting with one or more numeric characters followed by alphanumeric characters can convert to a Number, with Number that will not succeed. As in:
parseFloat('3.23abc'); //=> 3.23
Number('3.23abc'); //=> NaN
In both conversions, the input string is trimmed, by the way:
parseFloat(' 3.23abc '); //=> 3.23
Number(' 3.23 '); //=> 3.23

No. Both will result in the internal ToNumber(string) function being called.
From ES5 section 15.7.1 (The Number Constructor Called as a Function):
When Number is called as a function rather than as a constructor, it performs a type conversion...
Returns a Number value (not a Number object) computed by ToNumber(value) if value was supplied, else returns +0.
From ES5 section 15.1.2.3 (parseFloat (string)):
...
If neither trimmedString nor any prefix of trimmedString satisfies the syntax of a StrDecimalLiteral (see 9.3.1)
...
And 9.3.1 is the section titled "ToNumber Applied to the String Type", which is what the first quote is referring to when it says ToNumber(value).
Update (see comments)
By calling the Number constructor with the new operator, you will get an instance of the Number object, rather than a numeric literal. For example:
typeof new Number(10); //object
typeof Number(10); //number
This is defined in section 15.7.2 (The Number Constructor):
When Number is called as part of a new expression it is a constructor: it initialises the newly created object.

Not a whole lot of difference, as long as you're sure there's nothing but digits in your string. If there are, Number will return NaN. Another problem that you might get using the Number constructor is that co-workers might think you forgot the new keyword, and add it later on, causing strict comparisons to fail new Number(123) === 123 --> false whereas Number(123) === 123 --> true.
In general, I prefer to leave the Number constructor for what it is, and just use the shortest syntax there is to cast to an int/float: +numString, or use parse*.

When not using new to create a wrapper object for a numerical value, Number is relegated to simply doing type conversion from string to number.
'parseFloat' on the other hand, as you mentioned, can parse a floating point number from any string that starts with a digit, a decimal, or +/-
So, if you're only working with strings that contain only numerical values, Number(x) and parseFloat(x) will result in the same values

Please excuse me posting yet another answer, but I just got here via a Google search and did not find all of the details that I wanted. Running the following code in Node.js:
var vals = ["1", "1.1", "0", "1.1abc", "", " ", null];
for(var i = 0; i < vals.length; i++){
var ifTest = false;
if(vals[i])
{
ifTest = true;
}
console.log("val=" + vals[i] + ", Number()=" + Number(vals[i])+ ", parseFloat()=" + parseFloat(vals[i]) + ", if()=" + ifTest);
}
gives the following output:
val=1, Number()=1, parseFloat()=1, if()=true
val=1.1, Number()=1.1, parseFloat()=1.1, if()=true
val=0, Number()=0, parseFloat()=0, if()=true
val=1.1abc, Number()=NaN, parseFloat()=1.1, if()=true
val=, Number()=0, parseFloat()=NaN, if()=false
val= , Number()=0, parseFloat()=NaN, if()=true
val=null, Number()=0, parseFloat()=NaN, if()=false
Some noteworthy takeaways:
If protecting with an if(val) before trying to convert to number, then parseFloat() will return a number except in the whitespace case.
Number returns a number in all cases except for non-numeric characters aside from white-space.
Please feel free to add any test cases that I may be missing.