multisign.js

var ripple = require('ripple-lib').RippleAPI

const api = new ripple.RippleAPI({
  server: 'wss://s.altnet.rippletest.net'
});

api.connect().then(() => {

  const account = 'rDd6FpNbeY2CrQajSmP178BmNGusmQiYMM'
  api.prepareSettings(account, {
    signers: {
      threshold: 3,
      weights: [{
        address: 'rato1hAeQjm3FDRZ3J1vygZM3Y435wsGgw',
        weight: 1
      }, {
        address: 'rKL8nYYZmNXkKoT2tCJCnAAnuwQkKGPTur',
        weight: 1
      }, {
        address: 'rLHjNdeABJfbyYxXN1rSQzQ3Ne2Xjpyx2c',
        weight: 1
      }]
    }
  }).then(tx => {

    console.log(JSON.stringify(JSON.parse(tx.txJSON), null, 2))
    
    const {signedTransaction} = api.sign(tx.txJSON, 's**************************');

    console.log(signedTransaction)

    return api.submit(signedTransaction)
  }).then(res => { console.log(res) })
  .catch(error => {
    console.log(error)
  })
}).catch(error => {
  console.log(error)
})