Can anyone explain this code......?

See more:

Javascript

ES6

const BigNumber = require('bignumber.js')

const bigSorting = arr => arr.sort( (a, b) => new BigNumber(a).comparedTo(new BigNumber(b)) )

This is code above is online solution of hackerrank bignumber sorting......but here that guy uses compredTo() method which is not present in javascript....but still program run how ?

What I have tried:

function bigSorting(unsorted) {

    
    return unsorted.sort(function(a,b)
    {
        return a -b;
    });

}

This above is my code passes only 7 test cases out of 9....Of big number sorting