The snippet for building a tx body

txBody.js

// Using thor-devkit.js
const Transaction = require('thor-devkit/dist/transaction').Transaction

// Construct transaction body.
const txBody = {
    // Test-net: 0x27,  Main-net: 0x4a.
    chainTag: 0x27,
    // After which block this tx should happen?
    // 16 characters of block ID.
    blockRef: '0x004984e1064ed410',
    // Expires after 30 days.
    expiration: 30 * 8640,
    // Call the contract method "increaseAmount"
    clauses: [{
        to: '0x6d48628bb5bf20e5b4e591c948e0394e0d5bb078',
        value: 0,
        data: '0x74f667c4'
    }],
    gasPriceCoef: 0,
    gas: 50000,
    dependsOn: null,
    nonce: '0xa3b6232f', // Random number
    // Must include this field to activate VIP-191.
    reserved: { 
        features: 1
    }
}

// Construct a transaction.
const tx = new Transaction(txBody)