I have few number which I want to convert into string or BigInt because I want to send that number into smart contract but it automatically rounds the number

a = 10000000000000000000010; 
convertIntoStringWithoutChangingNumber(a) //'10000000000000000000010' => this should be string

sample inputs and outputs :
10000000000000000000020 // '10000000000000000000020'
10000000000000000001900 // '10000000000000000001900'
10100000000000000000000 // '10100000000000000000000'

I have tried few function but it all rounds off the last numeric value to 0. Simply need any way to convert this number into string without altering any digits.