//This is a private wrapper library that does all the zkstuff
const zkp = new (require('../lib/zkproof')).ZKProof("Ecdh");

const ff = require('ffjavascript');
const blake = require('blake-hash');
const jsCrypt = require('@iden3/js-crypto');
function toHex(number, length = 32) {
    const str = number instanceof Buffer ? number.toString('hex') : BigInt(number).toString(16)
    return '0x' + str.padStart(length * 2, '0')
}

console.log(blake)
const skBuff1 = jsCrypt.Hex.decodeString('0001020304050607080900010203040506070809000102030405060708090001');
const skBuff2 = jsCrypt.Hex.decodeString('0005020304050607080900010203040506070809000102030405060708090002');

const privateKey1 = new jsCrypt.PrivateKey(skBuff1);
const privateKey2 = new jsCrypt.PrivateKey(skBuff2);

const pubKey1 = privateKey1.public();
const pubKey2 = privateKey2.public();

const formatPrivKeyForBabyJub = (privKey) => {
    const sBuff = jsCrypt.Eddsa.pruneBuffer(
        blake('blake512').update(privKey.hex(), 'hex').digest()
    )
    const s = ff.Scalar.fromRprLE(sBuff, 0, 32)
    return ff.Scalar.shr(s, 3)
}



(async() => {    
    
   var result1 = await zkp.generateProof({
        privKey: toHex(formatPrivKeyForBabyJub(privateKey1)),
        pubKey: pubKey2.p.map(a => toHex(a))
    });

    var result2 = await zkp.generateProof({
        privKey: toHex(formatPrivKeyForBabyJub(privateKey2)),
        pubKey: pubKey1.p.map(a => toHex(a))
    });
    console.log(result1.publicSignals, result2.publicSignals);
    console.log(result1.publicSignals[0] == result2.publicSignals[0])
    console.log(result1.publicSignals[1] == result2.publicSignals[1])

})()

The circom circuit:

pragma circom 2.0.0;
include "../node_modules/circomlib/circuits/bitify.circom";
include "../node_modules/circomlib/circuits/escalarmulany.circom";

template Ecdh() {
    // Note: the private key needs to be hashed and pruned first
    signal input privKey;
    signal input pubKey[2];
    signal output sharedKey[2];

    component privBits = Num2Bits(253);
    privBits.in <== privKey;

    component mulFix = EscalarMulAny(253);
    mulFix.p[0] <== pubKey[0];
    mulFix.p[1] <== pubKey[1];

    for (var i = 0; i < 253; i++) {
        mulFix.e[i] <== privBits.out[i];
    }

    sharedKey[0] <== mulFix.out[0];
    sharedKey[1] <== mulFix.out[1];
}

component main{public [pubKey]} = Ecdh();