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Assigning BigInt stores wrong number (number+1)

I want to define a BigInt number in JavaScript. But when I assign it, the wrong number is stored. In fact 1 is added to the number when storing.
let num = BigInt(0b0000111111111111111111111111111111111111111111111111111111111111)
console.log(num) // Output: 1152921504606846976n
console.log(num.toString(2)) // Output: 1000000000000000000000000000000000000000000000000000000000000
So the number stored is 1152921504606846976, but it should be 11529215046068469765. Why is that?

Converting a Number to a BigInt can't create bits that weren't there before.
0b1 (just like 1) is a Number literal, so it creates a Number.
0b1n (just like 1n) is a BigInt literal, so it creates a BigInt.
By writing BigInt(0b1), you're first creating a Number and then converting that to a BigInt. As long as the value is 1, that works just fine; once the value exceeds what you can losslessly store in a Number [1], you'll see that the value of the final BigInt won't match the literal you wrote down. Whether you use binary (0b...), decimal, or hex (0x...) literals doesn't change any of that.
(And just to be extra clear: there's no reason to write BigInt(123n), just like you wouldn't write Number(123). 123n already is a BigInt, so there's nothing to convert.)
A simple non-BigInt way to illustrate what's happening is to enter 12345678901234567890 into your favorite browser's DevTools console: you can specify Number literals of any length you want, but they'll be parsed into an IEEE754 64-bit "double", which has limited precision. Any extra digits in the literal simply can't be stored, though of course each digit's presence affects the magnitude of the number.
[1] Side note: this condition is more subtle than just saying that Number.MAX_SAFE_INTEGER is the threshold, though that constant is related to the situation: any integral number below MAX_SAFE_INTEGER can be stored losslessly, but there are plenty of numbers above MAX_SAFE_INTEGER that can also be represented exactly. Random example: 1e20.

Issue with combining large array of numbers into one single number

I am trying to convert an array of numbers into one single number, for example
[1,2,3] to 123.
However, my code can't handle big arrays since it can’t return exact number. Such as
[6,1,4,5,3,9,0,1,9,5,1,8,6,7,0,5,5,4,3] returns 6145390195186705000
Is there any way that I could properly convert into a single number.I would really appreciate any help.
var integer = 0;
var digits = [1,2,3,4]
//combine array of digits into int
digits.forEach((num,index,self) => {
integer += num * Math.pow(10,self.length-index-1)
});

The biggest integer value javacript can hold is +/- 9007199254740991. Note that the bitwise operators and shift operators operate on 32-bit ints, so in that case, the max safe integer is 2^31-1, or 2147483647.
In my opinion, you can choose one of the following:
store the numbers as strings and manipulate them as numbers; you might have to implement special functions to add/subtract/multiply/divide them (these are classic algorithmic problems)
use the BigInt; BigInts are a new numeric primitive in JavaScript that can represent integers with arbitrary precision. With BigInts, you can safely store and operate on large integers even beyond the safe integer limit. Unfortunately, they work only with Chrome right now. If you want to work with other browsers, you might check this or even this if you work with angularjs or nodejs.
Try the following code in the Chrome's console:
let x = BigInt([6,1,4,5,3,9,0,1,9,5,1,8,6,7,0,5,5,4,3].join(''));
console.log(x);
This will print 6145390195186705543n. The n suffix marks that it is a big integer.
Cheers!

You can use JavaScript Array join() Method and parse it into integer.
Example:
parseInt([6,1,4,5,3,9,0,1,9,5,1,8,6,7,0,5].join(''))
results:
6145390195186705
Edited: Use BigInt instead of parseInt , but it works only on chrome browser.

The largest number possible in Javascript is
+/- 9007199254740991
Use BigInt. Join all numbers as a string and pass it in BigInt global function to convert it into int
var integer = 0;
var digits = [1,2,3,4]
//combine array of digits into int
digits.forEach((num,index,self) => {
integer += num;
});
integer= BigInt(integer);
Note : Works only on Chrome as of now. You can use othee libraries like BigInteger.js or MathJS

How to differentiate between binary and hexadecimal values

Let's say that I needed the user to enter a binary or hexadecimal value and the program would take it from there. Is there a way to differentiate whether the value they entered is binary or hexadecimal?
I thought I had it figured out by checking if the string contained letters or numbers above 1 but what about in the case of 101101 or other similar hex inputs? Is it even possible to know without any other context?
For the sake of including failed attempts I tried the following to check if the string contained letters which hexadecimal values could:
if (Number.isInteger(parseInt(input)))
but other than it not solving the above problem (since hex values don't always have letters), it also fails because it still returns true when letters are mixed into the input as it still parses an integer one way or another.

Is it even possible to know without any other context?
No, it's not. Programming languages often allow number literals in various numeral systems but they have to be marked accordingly. In JavaScript:
No prefix: decimal. Example: 12345
0b prefix: binary. Example: 0b10101
0o prefix: octal. Example: 0o123
0x prefix: hexadecimal. Example: 0x12345
You could require the same notation for the input, or you provide another control that allows the user to choose the system (you could still internal prefix the input correctly).
For completeness, here is a function that would convert any of these inputs to numbers:
const radixTable = {
'0b': 2,
'0o': 8,
'0x': 16,
};
function convert(str) {
let radix = 10;
if (radixTable.hasOwnProperty(str.slice(0, 2))) {
radix = radixTable[str.slice(0,2)];
str = str.slice(2);
}
return parseInt(str, radix);
}
['12', '0b1100', '0o14', '0xC'].forEach(
str => console.log(`${str}:`, convert(str))
);

I'm not aware of JavaScript having a lot of advanced math capabilities built in. If it was oriented toward that end, it would probably have more numeric variable types to give you larger numbers like a double or long. You might want to create an object that would have a property to set whether the number in the object is hex or decimal, and then the value.
let numberObj = {
numberSystem: 'decimal',
value: '4505'
}

Which javascript function can be used to covert an array of characters into a number?

There are a few Javascript functions available to convert anything into its equivalent number. Number() operates on an Object, valueOf(), parseFloat, parseInt() are also available.
I have an array which stores numbers 0-9 and decimal point, the elements of the array taken together represents a number. What is the best way to convert this array into a number, whole or fractional?
EDIT: Apologies if I were not clear before. The array, holding the 0-9 characters and possibly a decimal point, could represent either a whole number(without the decimal obviously) or a fractional number. So please suggest something that works for both cases. Thanks.

Try this
var a = [1,2,3,".",2,3];
var num = +a.join("");

What is the best way to convert this array into a number, whole or fractional?
Firstly to combine your array elements you should use Array.join().
You will then have a concatenated variable of your values and decimal. To convert this to a whole number, use parseInt(), and to a floating point number use parseFloat(). You can use the unary + operator (which acts similarly to parseFloat), however in my opinion it is not the best choice semantically here, as you seem to want a specific type of number returned.
Example:
var arr = ['1','.','9','1'];
var concat = arr.join();
var whole = parseInt(concat);
var floating = parseFloat(concat);
Also, parseInt will trim the decimal portion of your number, so if you need rounding you can use:
var rounded = Math.round(parseFloat(concat));

You could use the split property of the string. It splits all the characters into an zero based array.
var charSplits = "this is getting split.";
var splitArr = charSplits.split();
Console.log(splitArr);
// this returns i
Console.log(splitArr[2]);

Currency Math in JavaScript

Can someone please help me out with a JavaScript/jQuery solution for this arithmetic problem:
I need to subtract one number from the other.
The problem is that the numbers have a dollar sign (because its money), therefore jQuery is treating them as strings instead of numbers.
I have created two variables - toalAssets and totalLiabilites. I would like to subtract the latter from the former and place the result into another variable called netWorth.
Perhaps i need to use parseFloat()?
But I'm not sure how - This is all a little over my head!

var totalLiabilites = '$52.34';
var toalAssets = '$85.12';
var pattern = /[^0-9.-]+/g;
var result = parseFloat(toalAssets.replace(pattern, '')) -
parseFloat(totalLiabilites.replace(pattern, ''));
// result: 32.78
Note: In JavaScript it is recommended1 to handle money as an integer representing the number of cents (8512 instead of 85.12). This is to avoid problems with floating-point arithmetic. 0.1 + 0.2 == 0.3 returns false in JavaScript, but fortunately integer arithmetic in floating point is exact, so decimal representation errors can be avoided by scaling.
You may want to check the following post for further reading on this topic: Is JavaScript’s math broken?
You can always apply the currency-sign formatting when the values are rendered to the browser.
1Douglas Crockford: JavaScript: The Good Parts: Appendix A - Awful Parts (page 105).

parseFloat() won't work because your string begins with a non-number, the dollar sign.
You can simply do a replace to remove the dollar sign, along with a parseFloat to get the value:
totalAssets = parseFloat(totalAssets.replace('$', ''));
totalLiabilities = parseFloat(totalLiabilities.replace('$', ''));
var difference = '$' + (totalAssets - totalLiabilities);
This code replaces your original strings with floats. You could load them into new variables as well. Likewise, difference does not have to have the '$' prepended.

var a = "$20";
var b = "$34";
var c = parseFloat(a.replace(/[^0-9\.]+/g, "")) - parseFloat(b.replace(/[^0-9\.]+/g, ""));
alert(c);