I have a scenario where I need to parsefloat 19 digit string to number.
e.g. parseFloat("1000000000100000043") gives me 1000000000100000000
but the expected output required is 1000000000100000043
This is likely a precision overflow error.
The Number data type (but also int and float in other languages) have a finite number of bits available to represent a number. Typically around 15-16 decimal digits worth.
When length of original number in the string exceeds available precision, such number can no longer be represented by the target data type.
In this case the parseFloat function fails silently. If you want to catch this situation you need to add code to check incoming data or use another function, possibly a custom one.
Alternatively, you can convert the numeric value back to string and compare it with original to detect a discrepancy.
See also a question regarding double.Parse
You are running into how Javascript numbers are stored. See, e.g., here: https://www.w3schools.com/js/js_numbers.asp
You can use a library like decimal.js to work with large, exact numbers. These libraries store the number as string, but allow you to do mathematical operations.
Related
I have a string "215.00".
I want to convert this to a number and when I do parseInt("215.00") it returns 215 as a number. I want it to be as a number 215.00.
To try and do this I did parseFloat("215.00").toFixed(2);, however this also returns a string. I have found many answers on here, but they all convert the number to a string. Does anyone know how to fix this?
Please see my code attempt below:
var number = "215.00";
parseFloat(number).toFixed(2);
I want to get 215.00 as opposed to "215.00"
I will post here this as an Answer, for future purpose.
If you want to represent the zeros on the right hand-side, you need to represent it as a string. Because the numerical value of 215.00 it is in fact 215, therefore it will not keep the two decimal places.
The parseFloat method would work for a number such as "215.01", where it would parse it to the numerical value of 215.01.
I have the problem that when i round a number to 2 decimals the parseFloat() function removes .00 from the number. I have tried
var num = parseFloat(Math.round(19 * 100) / 100).toFixed(2);
The return: num="19.00"
The return i need: num = 19.00
I know 19 = 19.00, but i am using a service that always require two decimals .00
The function returns a string with the right value. When i parse it to float the .00 is removed.
You cannot get 19.00 as float, only as string, because numbers always remove trailing zeros.
Maybe you can show us a bit more code to get an idea, there you need these trailing zeros?
Numbers do and can not hold information about their representation. They are only a numerical value.
When you display a number using window.alert, console.log or similar, you are not looking at a number, but at a string. Those display functions convert numbers to strings before displaying them. Number.toFixed also converts numbers into strings, with the difference being that it rounds them to two decimal places, so you end up with another representation of the same number.
What I am trying to say is that to display a number, you cannot get around converting it to a string. Whether you do it explicitly or the display function does it for you. When you send the number to the service that you are using, you are probably also sending a string (JSON, XML, etc. are always strings once you send them). If you need the value of the number for calculations, use it, then convert it in the end. No matter how, you have to do it in the end if you want those 0's at the end.
In my case, i am converting a string value of '9999999999999999' to integer using parseFloat(). But it converts to next number of it i.e. 10000000000000000. But i need to convert it to before of that number i.e. 999999999999999998. I have searched for a while in google. But could not get clear idea to implement this.
Try this
document.getElementById("demo").innerHTML=Math.round(9999999999999999-2);
OUTPUT
9999999999999998
This number is too big to represented precisely in JavaScript Number value. So no amount of conversion will give you values reliably/precisly as you want around such range.
I.e. (9999999999999999-1)===(9999999999999999) returns true, but (9999999999999998)===(9999999999999999) returns false.
If you need such high precision in JavaScript (similar to many other languages) you need to use specialized data types (unfortunately there is no "BigInteger" type built in in JavaScript).
You will need to use some external javascript library to work with big numbers like that, cause max number you cant represent without losing presicion in javascript integers is 9007199254740992 (Explanation : What is JavaScript's highest integer value that a Number can go to without losing precision?)
Here you have some link where people discuss about some libraries to use for javascript big numbers.
How to deal with big numbers in javascript
I am working on a calculator in javascript, where user can enter the values in textfield and operation will be performed.
Now if user enters a very large value
for example 5345345345353453453453535
it is converted to 5.345345345353453e+24
I am using parsrInt() to convert it to integers. and it gives me 5.
which is wrong .
Can anybody suggest how to solve it?
Integers in javascript are, like every numbers, stored as IEEE754 double precision floats.
So you can only exactly store integers up to 2^51 (the size of the mantissa).
This means you'll have to design another format for dealing with big integers, or to use an existing library like BigInteger.js (Google will suggest a few other ones).
Taken from Mozilla documentation:
Parses a string argument and returns an integer of the specified radix
or base.
Therefore parseInt() is taking your value as a string 5.345345345353453e+24
It is then ignoring any non-integer values and classing this as a decimal (5.345...) and then evaluating this to 5.
As #dystroy has pointed out, if you wish to carry out calculations with these large numbers you'll need to use a custom format, or use a pre-existing javascript library.
Try parseFloat instead of parseInt.
<script type="text/javascript">
var value = parseFloat(5345345345353453453453535);
alert(value);
</script>
I'm transferring raw data like [{id: 12000000000002539, Name: "Some Name"}] and I'm getting the object [{id: 12000000000002540, Name: "Some Name"}] after parsing, for now server side converting id into string seems to help.
But is there a better way to transfer bigint data correctly?
The value is actually not exceeding the maximum numeric value in JavaScript (which is "only" 1.7308 or so).
However, the value is exceeding the range of "integral precision". It is not that the wrong number is sent: rather, it is that the literal 12000000000002539 can only be represented as precisely as 12000000000002540, and thus there was never the correct numeric value in JavaScript. (The range of integrals is about +/- 253.)
This is an interesting phenomena of using a double relative-precision (binary64 in IEEE-754 speak) type to store all numeric values, including integers:
12000000000002539 === 12000000000002540 // true
The maximum significant number of decimal digits that be precisely stored as a numeric value is 15 (15.95, really). In the above, there are 17 significant digits, so some of the least-significant information is silently lost. In this case, as the JavaScript parser/engine reads in the literal value.
The only safe way to handle integral numbers of this magnitude in JavaScript is to use a string literal or to break it down in another fashion (e.g. a custom numeric type or a "bigint library"). However, I recommend just using a string, as it is human readable, relatively compact (only two extra characters in JSON), and doesn't require special serialization. Since the value is just an "id" in this case, I hope that math does not need to be performed upon it :)
Happy coding.