Helios API/ Example: PicoSwap/

Contract helper class

Before describing PicoSwap's smart contract end-points, it is helpful to define a Contract class that can be instantiated for each set of UTxOs locked at the script address having the same datum.

class Contract {
     * @param {helios.ConstrData} datum - not a helios.Datum instance!
     * @param {helios.UTxO[]} utxos
    constructor(datum, utxos) {
        this.datum = datum
        this.utxos = utxos

    get seller() {
        return new helios.PubKeyHash(this.datum.fields[0].bytes)

    get sellerAddress() {
        // true -> testnet
        return helios.Address.fromPubKeyHash(true, this.seller)

    get price() {
        return helios.Value.fromData(this.datum.fields[1])

    get forSale() {
        return helios.UTxO.sumValue(this.utxos)

    get nonce() {
        return this.datum.fields[3].int

Note: ConstrData is one of the 5 child-types of UplcData. The other UplcData child-types are: IntData, ByteArrayData, ListData and MapData.

Grouping the contract UTxOs and extracting the inline datum data is left as an exercise to the reader.