How to use the jsbn.BigInteger.prototype function in jsbn

// Basic Javascript Elliptic Curve implementation
// Ported loosely from BouncyCastle's Java EC code
// Only Fp curves implemented for now

// Requires jsbn.js and jsbn2.js
var BigInteger = require('jsbn').BigInteger
var Barrett = BigInteger.prototype.Barrett

// ----------------
// ECFieldElementFp

// constructor
function ECFieldElementFp(q,x) {
    this.x = x;
    // TODO if(x.compareTo(q) >= 0) error
    this.q = q;
}

function feFpEquals(other) {
    if(other == this) return true;
    return (this.q.equals(other.q) && this.x.equals(other.x));
}

}
    }

    function _bi2bytes(n, cnt) {
        if (cnt === undefined) {
            cnt = (n.bitLength() + 7) >>> 3;
        }
        var bytes = new Array(cnt);
        for (var i = cnt - 1; i >= 0; i--) {
            bytes[i] = n[0] & 255; // n.and(0xff);
            n = n.shiftRight(8);
        }
        return bytes;
    }

    BigInteger.prototype.bytes = function(n) {
        return _bi2bytes(this, n);
    };

    // /////////////////////////////////////////////////////////

    function _bytehash(s) {
        var sha = crypto.createHash('sha512').update(s).digest();
        return _bi2bytes(_bi(sha), 64).reverse();
    }

    function _stringhash(s) {
        var sha = crypto.createHash('sha512').update(s).digest();
        return _map(_chr, _bi2bytes(_bi(sha), 64)).join('');
    }

    function _inthash(s) {

// Basic Javascript Elliptic Curve implementation
// Ported loosely from BouncyCastle's Java EC code
// Only Fp curves implemented for now

// Requires jsbn.js and jsbn2.js
var BigInteger = require('jsbn').BigInteger
var Barrett = BigInteger.prototype.Barrett

// ----------------
// ECFieldElementFp

// constructor
function ECFieldElementFp(q,x) {
    this.x = x;
    // TODO if(x.compareTo(q) >= 0) error
    this.q = q;
}

function feFpEquals(other) {
    if(other == this) return true;
    return (this.q.equals(other.q) && this.x.equals(other.x));
}