Working with Smart Contracts

Taquito allows developers to interact with Smart Contracts as if they are "Plain Old Javascript Objects".

The "Machine Language" of Tezos Smart Contracts is named Michelson. Michelson is a stack-based language that is human-readable. It's possible to author Smart-Contracts directly in Michelson. However, developers can use High-Level Languages (such as Ligo or SmartPy) to write smart contracts.

Taquito makes developing applications (dApps or traditional programs) around a Tezos Smart Contract easy. Taquito can also "originate" (create) a new Smart Contract to the Tezos Blockchain.

Michelson is a somewhat specialized language that isn't typical in Javascript or Typescript development contexts. Taquito helps to bridge the gap between the Tezos blockchain and a typical Javascript or Typescript development environment.

Taquito's Smart Contract Abstraction#

Taquito assists developers by reading the Michelson code for a given contract from the blockchain. Based on the retrieved Michelson code, Taquito generates a contract javascript object with methods and storage that correspond to the contract's Michelson entrypoints, storage definitions and values.

The Counter Contract#

In this guide, we use a straightforward "counter" smart contract to illustrate how Taquito works.

The counter contract has two entrypoints named increment and decrement. These entrypoints are used by Taquito to generate corresponding javascript methods that are available to the developer.

The counter contracts storage is a simple integer that gets increased or decreased based on the calls to the entrypoints.

Counter Contract in CameLIGO#

type storage = int
(* variant defining pseudo multi-entrypoint actions *)
type action =
| Increment of int
| Decrement of int
let add (a,b: int * int) : int = a + b
let sub (a,b: int * int) : int = a - b
(* real entrypoint that re-routes the flow based on the action provided *)
let main (p,s: action * storage) =
 let storage =
   match p with
   | Increment n -> add (s, n)
   | Decrement n -> sub (s, n)
 in ([] : operation list), storage

You can view this contract and deploy it to a testnet using the Ligo WebIDE

Counter Contract Michelson source code#

{ parameter (or (int %decrement) (int %increment)) ;
  storage int ;
  code { DUP ;
         CDR ;
         DIP { DUP } ;
         SWAP ;
         CAR ;
         IF_LEFT
           { DIP { DUP } ;
             SWAP ;
             DIP { DUP } ;
             PAIR ;
             DUP ;
             CAR ;
             DIP { DUP ; CDR } ;
             SUB ;
             DIP { DROP 2 } }
           { DIP { DUP } ;
             SWAP ;
             DIP { DUP } ;
             PAIR ;
             DUP ;
             CAR ;
             DIP { DUP ; CDR } ;
             ADD ;
             DIP { DROP 2 } } ;
         NIL operation ;
         PAIR ;
         DIP { DROP 2 } } }

Loading the contract in Taquito#

To load the contract from the Tezos Blockchain, we use the Tezos.contract.at method. We can inspect the contract methods and data types using the c.parameterSchema.ExtractSignatures() method.

The following example shows how to load the contract, and view the methods on that contract.

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Result

The at() method causes Taquito to query a Tezos nodes RPC API for the contracts "script" and "entrypoints". From these two inputs, Taquito builds an ordinary JavaScript object with methods that correspond to the Smart Contracts entrypoints.

The at method returns a representation of the contract as a plain old javascript object. Taquito dynamically creates an increment and decrement method that the developer can call as follows:

  • contract.methods.increment()
  • contract.methods.decrement()

In Tezos, to call an entrypoint on a contract, one must send a transfer operation. In the case of the counter contract, the transfer value can be 0 as the contract does not expect to receive any tokens. To call the increment entrypoint, the transfer must have the appropriate Michelson values specified as "params".

We can inspect the transfer params produced by Taquito using the toTransferParams() method as follows.

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Result

Calling the Increment function#

In the next example, we call the send() method. This example requires an additional ceremony for getting a temporary key for signing.

We call the send() method on the increment() method. Taquito then forges this operation into a transfer operation (with a transfer value of zero), signs the operation with our testing key, and injects or broadcast the operation to the Tezos RPC node.

Then we wait for the confirmation(3) to complete. The 3 number tells Taquito how many confirmations to wait for before resolving the promise. 3 is a good value for this type of demonstration, but we recommend a higher value if you are dealing with mainnet transactions.

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Result