Adding two big numbers in javascript [duplicate] - javascript

This question already has answers here:
How to deal with big numbers in javascript [duplicate]
(3 answers)
Closed 3 years ago.
I've been trying to add the following numbers using javascript;
76561197960265728 + 912447736
Sadly, because of rounding in javascript it will not get the correct number, I need the number as a string.
I've tried removing the last few digits using substr and then adding the two numbers together and then putting the two strings together, sadly this doesn't work if the first of the number is a 1.
function steamid(tradelink){
var numbers = parseInt(tradelink.split('?partner=')[1].split('&')[0]),
base = '76561197960265728';
var number = parseInt(base.substr(-(numbers.toString().length + 1))) + numbers;
steamid = //put back together
}
steamid('https://steamcommunity.com/tradeoffer/new/?partner=912447736&token=qJD0Oui2');
Expected:
76561198872713464

For doing operations with such big integers, you should use BigInt, it will correctly operate on integers bigger than 2ˆ53 (which is the largest size that normal Number can support on JS
const sum = BigInt(76561197960265728) + BigInt(912447736);
console.log(sum.toString());
Edit 2020: This API still not widely supported by some browsers, so you may need to have a polyfill, please check this library

Related

Javascript array join does not work correctly [duplicate]

This question already has answers here:
Issue with combining large array of numbers into one single number
(3 answers)
Closed 1 year ago.
I have the following array and I want to join it into a number
const arr = [6,1,4,5,3,9,0,1,9,5,1,8,6,7,0,5,5,4,3]
const digits = arr.join("") //6145390195186705543
const digitsToNumber = +arr.join("") //6145390195186705000
console.log(digits);
console.log(digitsToNumber);
You can see that the join function works. However, when I try to convert it into a number, it shows a weird value. Do you guys know why it happened that way?
As stated in the comments, the value is too large for JavaScript and is truncated.
We can use BigInt to prevent this. Use with caution!
const arr = [6,1,4,5,3,9,0,1,9,5,1,8,6,7,0,5,5,4,3]
const digits = arr.join('');
const digitsToNumber = +arr.join("");
const bigDigitsToNumber = BigInt(arr.join(''));
console.log(digits); // 6145390195186705543
console.log(digitsToNumber); // 6145390195186705000
console.log(bigDigitsToNumber.toString()); // 6145390195186705543
They will log different results because you are exceeding Number.MAX_SAFE_INTEGER - the highest value JS can safely compare and represent numbers.
One method to check if you are ever exceeding the limit (besides remembering the value) is Number.isSafeInteger()
Number.isSafeInteger(digitsToNumber); //false
From the docs: For larger integers, consider using the BigInt type.
To convert your concatenated string into a number you could use parseInt("123") method.
const number= parseInt(digitsToNumber)
However because of your number is too big or could be bigger, Javascript can not handle that numbers which contains more than 16 digit. If you also have a problem like that you can use some external big number libraries like BigNumber.Js.
Edit: According to Teemu's comment, you could also use link native big integer handling library.

Is there a better way to achieve this? '000000'.slice(0, -'434'.length) + '434' = '000434' [duplicate]

This question already has answers here:
convert '1' to '0001' in JavaScript [duplicate]
(4 answers)
Pad a number with leading zeros in JavaScript [duplicate]
(9 answers)
Closed 3 years ago.
Yep, the title says pretty much everything. Basically I want a default X-digit number which is all zeros. Then, from this number, I want to replace the last characters with other numbers. For example, if I have '434', and the default is '000000', the result should be '000434'.
In Ruby, this is the equivalent of doing '%.6d' % 434 and it returns '000434'. If the number I want to save has more than 6 digits, I just use that number instead. I realized that as I'm working with strings I could use this solution:
let base = '000000'
let str = '434'
console.log(base.slice(0, -str.length) + str)
Buuut, even if it's a simple approach, I don't know if it's the best. What daya' think?
For compatibility with older JS environments, you can depend only on a simpler slice:
(base + str).slice(-6)
For modern ones, padStart is available:
str.padStart(6, '0') // or String(num)
JavaScript has string.padStart(length, padString)
let str = '434'
const updated = str.padStart(6, '0')
console.log(updated)

JS how to add instead of concatenate numbers [duplicate]

This question already has answers here:
Javascript variables not adding two variables correctly, only concatenating
(3 answers)
Closed 4 years ago.
This question has an answer:
see - Javascript variables not adding two variables correctly, only concatenating
I am trying to add 5 units to a number but the number is being concatenated instead.
this.graphicState[i].shapes[j][k].x += 5
Each time this is run in a loop the outputs are
105.00
105.005
105.0055
105.00555
...
The output I am looking for is,
105.00
110.00
115.00
120.00
...
I tried,
this.graphicState[i].shapes[j][k].x += parseFloat(5)
I also tried this, but get the same results,
this.graphicState[i].shapes[j][k].x = this.graphicState[i].shapes[j][k].x + 5
Thanks,
You need to convert any/all string values to numbers in an expression that has strings as operands with + as the operator. The 5 isn't the issue, this is:
this.graphicState[i].shapes[j][k].x
So, that's what needs to be converted. You can do that easily by prepending a + to it:
+this.graphicState[i].shapes[j][k].x;
Do the conversion on the string first and then use the converted value in your mathematical expression. Here's a simplified example:
var result = "5"
result = +result + 10;
console.log(result);
Try this method
this.graphicState[i].shapes[j][k].x = (parseFloat(this.graphicState[i].shapes[j][k].x) + 5).toFixed(2);

Smaller number is greater than bigger number [duplicate]

This question already has answers here:
Why parseFloat in javascript returns string type for me?
(2 answers)
Closed 4 years ago.
In my JS, I'm doing a check to see if one number is greater than the other. I'm attaching the image of Chrome DevTools:
As you can see here, the code has made it inside the if statement. On the right, in the Watch, you can see amount = "3.00" and available = "261.60".
What would cause the smaller number to be greater than the bigger number?
You are are comparing strings. In the code you are calling parseFloat, which is the right idea, but it's followed by toFixed(). toFixed() returns a string.
console.log(typeof parseFloat("3.00").toFixed(2))
You need to make sure you're comparing numbers. An easy way is:
if(+amount > +available)
Alternatively, don't call toFixed() until it's time to display the number.

javascript parseInt() failing? [duplicate]

This question already has an answer here:
What is the standard solution in JavaScript for handling big numbers (BigNum)?
(1 answer)
Closed 6 years ago.
n = "11004691915666669"
parseInt(n)
parseInt(n, 10)
Both results are: 11004691915666668
This is off by one. I tested some other values and they convert correctly. Is this a bug in the library or is there a better way to convert?
See this SO question for more details. Your value is beyond the maximum integer that Javascript can represent with full accuracy.
Under the hood Javascript doesn't understand integers, everything's floating point. You're hitting the reduced accuracy that happens when you get to very large numbers.
From the Javascript reference at MDN given here.
The integer range for a Number is defined as follows :
var biggestInt = 9007199254740992;
var smallestInt = -9007199254740992;
Which is why since your number exceeds the biggestInt value preset by Javascript, the parseInt method only returns the integer value that lies within the Integer range for a Number in Javascript as defined above.

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