This Ethereum smart contract demonstrates an 'Atomic cross-chain swap between different blockchain networks' and is based on the NEM cross-chain swap functionality. The blockchains needs to support Hashed TimeLock Contract or HTLC for a trustless environment for swaps. In NEM Blockchain these are described as 'secret lock' and 'secret proof' functionalities. It's possible with Ethereum, Bitcoin, NEM, NEO and several other protocols.
However, whether it is real 'Atomic' is a valid point to discuss. Nevertheless both parties have a strong incentive to fullfill the rules.
Lets say Alice wants to convert ETH to NEM:XEM and Bob NEM:XEM to Ether.
The steps required are illustrated in the diagram below. 
| Transaction | Network | Sender | |
|---|---|---|---|
| TX1 | secretLock(uint256 _lockTimeSec, bytes32 _hash, address _recipient) | Ethereum Rinkeby Testnet | Alice |
| TX2 | SecretLockTransaction.create(Deadline.create(), new Mosaic(new MosaicId('nem:xem'), exchangeValue), lockTime, HashType.SHA3_512, secret, aliceNEM.address, NetworkType.MIJIN_TEST) | NEM Catapult Private Chain | Bob |
| TX3 | SecretProofTransaction.create( Deadline.create(), HashType.SHA3_512, secret, proof, NetworkType.MIJIN_TEST) | NEM Catapult Private Chain | Alice |
| TX4 | secretProof(bytes32 _hash, bytes _proof) | Ethereum Rinkeby Testnet | Bob |
Hint: Note that the wording in this Ethereum smart contract is a bit different as in the NEM documentation. For some, the NEM naming can be confusing, because secret represents a hash of a proof. However, consider that the hashing algorithm also needs to be revealed for the swap to work and that's why it could be confused with the hash term.
Web3 version 1.x is installed with NPM. Also Truffle comes with Web3 0.2x. The API of these Web3 are not always compatible.
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