Here is how you can easily delegate SP and convert between VEST and STEEM programmatically

Earlier today I was trying to programmatically delegate to one of my accounts with the following (correct) code:

const client = new dsteem.Client('https://api.steemit.com');

const delegate = async (config) => {
  const {
    delegation, privateKey: privateActiveKey, delegator, delegatee,
  } = config;
  const privateKey = dsteem.PrivateKey.fromString(privateActiveKey);
  const op = [
    'delegate_vesting_shares',
    {
      delegator,
      delegatee,
      vesting_shares: delegation,
    },
  ];
  client.broadcast.sendOperations([op], privateKey).then(
    result => console.log('Delegation done.', JSON.stringify(result)),
    console.error,
  );
};

const config = {
  delegatee: 'bot-test',
  delegator: 'marcocasario',
  privateKey: '51111111111111111111111111111111111111111111111RlFx', // private active key
  delegation: '29456.000000 VESTS', // Around 15 SP
};
delegate(config);

Initially though I was passing in as input STEEM instead of VEST so the script was erroring out. After reading a bit around I found out how to easily convert one into the other. Here is the JS code:

  const cache = {
    totVestShares: null,
    totSteem: null,
  };
    
  const getProps = () => new Promise((res) => {
      fetch('https://api.steemit.com', {
        method: 'POST',
        cache: 'no-cache',
        credentials: 'omit',
        headers: {
          'Content-Type': 'application/json',
        },
        redirect: 'follow',
        referrerPolicy: 'no-referrer',
        body: JSON.stringify({
          jsonrpc: '2.0',
          method: 'condenser_api.get_dynamic_global_properties',
          params: [],
          id: 1,
        }),
      }).then(res => res.json()).then((data) => {console.log(data);res(data.result)});
  });
    
  // Usage: steemToVest('15 STEEM'); >> '29456.000000 VESTS'
  const steemToVest = async (steem) => {
    if (!cache.totSteem) {
      const { total_vesting_shares, total_vesting_fund_steem } = await getProps();
      cache.totVestShares = +total_vesting_shares.split(' ')[0];
      cache.totSteem = +total_vesting_fund_steem.split(' ')[0];
    }
    const steemAmount = +steem.split(' ')[0];
    const vests = steemAmount * cache.totVestShares / cache.totSteem;
    // Always 6 decimals and rounded
    const roundedVests = (Math.round(vests * 1000000 + Number.EPSILON) / 1000000).toFixed(6);
    console.log(`${steemAmount} STEEM is ${roundedVests} VESTS.`);
    return roundedVests;
  };
  
  // Usage: vestsToSteem('29456.61988576255 VESTS'); >> '15.000 STEEM'
  const vestsToSteem = async (vests) => {
    if (!cache.totSteem) {
      const { total_vesting_shares, total_vesting_fund_steem } = await getProps();
      cache.totVestShares = +total_vesting_shares.split(' ')[0];
      cache.totSteem = +total_vesting_fund_steem.split(' ')[0];
    }
    const vestsAmount = +vests.split(' ')[0];
    const steem = vestsAmount * cache.totSteem / cache.totVestShares;
    const roundedSteem = (Math.round(steem * 1000 + Number.EPSILON) / 1000).toFixed(3);
    console.log(`${vestsAmount} VESTS is ${roundedSteem} STEEM.`);
    // Always 3 decimals and rounded
    return roundedSteem;
  };

USAGE:

This is even easier than retrieving balances of a list of Steemit accounts or calculate an account's RC programmatically as there is no need to import SteemJs or SteemdJs for the VEST <=> STEEM conversion.

The script simply uses a cross domain http requests. This means that you can try this simple script in any webpage.

Step by step instructions:

STEP 1
Open your favorite browser on any site (I strongly recommend using Brave browser) and open the DevTools (Ctrl + Shift + J on Linux/Windows and Cmd + Opt + J on Mac).

STEP 2
Copy and paste my script above in the Console.

STEP 3
Press enter and there you go! You can now execute the 2 commands to convert between STEEM and VESTS.

Enjoy!! =]

NOTE:
As usual, this script is completely safe as it does not require any sort of keys to function and can be executed in any webpage!