Writing a smart contract in TypeScript (TS)

Learn how to write a smart contract in TypeScript (TS).

Prerequisites

Note:

Ensure you succesfully set up your dev environment.

Sample contract functionality

The sample contract serves as a demonstration of general QVM logic.

It is capable of:

registering users into the database
storing the last registered user's name in the database
echoing the previous user's name to STDOUT
incrementing the total registered user count
storing above counter in the database

Constructor logic

While some programming languages do not have explicit support for constructors you are free to implement your own logic for contract initialization after it gets deployed.

Your binary will be invoked with a single “construct” argument.

TypeScript (TS) smart contract sample

let maxUser = 100;

function construct() {
    if (process.env.DB_QVM_INITIALIZED === "true") {
        process.stderr.write("contract is already initialized\n");
        process.exit(1);
    }
    process.stdout.write("DBW=QVM_INIT_MAXUSER=" + maxUser);
    process.stdout.write("\n");
    process.exit(0);
}

function initialize() {
    if (process.env.DB_QVM_INITIALIZED !== "true") {
        process.stderr.write("contract is not initialized\n");
        process.exit(1);
    }
    maxUser = parseInt(process.env.DB_QVM_INIT_MAXUSER || "0");
}

function contract(args: String[]) {
    if (args && args.length === 1 && args[0] === "construct") {
        construct();
    }
    // THIS SAMPLE ONLY SUPPORTS THE "register" FUNCTION
    if (args && args.length === 2 && args[0] === "register") {
        initialize();
        // GET THE CURRENT USER'S NAME OR DEFAULT TO "unknown" IF THIS IS THE FIRST CALL
        const previous_name = process.env.DB_USER_CURRENT || "unknown";
        // GET THE TOTAL USER COUNT
        const total_user_count = parseInt(process.env.DB_TOTALUSERS || "0");
        if (total_user_count + 1 > maxUser) {
            process.stderr.write("exceeded max user\n");
            process.exit(1);
        }
        // WRITE PREVIOUS USER NAME TO STDOUT
        process.stdout.write("OUT=prevname: " + previous_name);
        process.stdout.write("\n");
        // UPDATE CURRENT USER NAME BY WRITING IT TO DB
        process.stdout.write("DBW=USER_CURRENT=" + args[1]);
        process.stdout.write("\n");
        // STORE USER NAME UNDER A STORAGE SLOT FOR PERSISTENCE (CURRENT GETS OVERWRITTEN ON EACH CALL)
        process.stdout.write("DBW=USER_" + total_user_count + "=" + args[1]);
        process.stdout.write("\n");
        // INCREMENT THE TOTAL USER COUNT
        process.stdout.write("DBW=TOTALUSERS=" + (total_user_count + 1));
        process.stdout.write("\n");
        process.exit(0);
    }
    if (args.length >= 1) {
        process.stderr.write("Wrong CMD: " + args[0]);
        process.stderr.write("\n");
        process.exit(1);
    }
    process.stderr.write("Wrong args!");
    process.stderr.write("\n");
    process.exit(1);
}

contract(process.argv.slice(2));

Save the contract

Open a text editor and save above sample contract as main.ts file.

Writing a smart contract in JavaScript (JS)

Writing a smart contract in C++

Contents

Prerequisites Sample contract functionality Constructor logic TypeScript (TS) smart contract sample Save the contract