How to undo the “toString()” function

Question

JavaScript's toString function has 1 parameter: the base. If I use (2) , then the output string will be in binary, (16) -> hex, (8) -> octal. These aren't the only bases it supports; it supports up to base 36.

1234567890n.toString(36)

The result of that expression is:

kf12oi

Since this is a pure unary function that doesn't result in data lost, I was guessing there is a way to undo it too, right?

I'm trying not to use the number prefixes such as 0b , 0x , or 0o , since they don't cover everything.

If the answer isn't cross compatible, it's still acceptable.

Update

Sorry, I forgot to mention, the input is actually a BigInt and is considered to be Infinity when using parseInt() .

Answer 1

Just parse the number back with:

parseInt('kf12oi', 36); // 1234567890

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If the number can't fit in the Number type. You should manually convert the number:

 parseBigInt = (value = '0', base = 10) => [].reduce.call(value, (acc, x) => acc * BigInt(base) + BigInt(parseInt(x, base)), 0n); valB10 = '1' + [...new Array(600)].map(x => Math.random() * 10 | 0).join(''); console.log('%s', BigInt(valB10)); valB36 = BigInt(valB10).toString(36); console.log(valB36); parsed = parseBigInt(valB36, 36); console.log('%s', parsed); console.log(BigInt(valB10) === parsed);

Answer 2

use parseInt to convert any radical number to the decimal

 let num = 23; let inBinary = num.toString(2); console.log(inBinary); let backtoDecimal = parseInt(inBinary, 2) console.log(backtoDecimal)