encodeABI.html

<script src="web3.min.js"></script>
<script>
  const web3 = new Web3();
  encodeABI = () => {
    document.querySelector('#result').innerText = '';
    const abi = JSON.parse(document.querySelector('#abi').value);
    const method = document.querySelector('#method').value;
    const contract = new web3.eth.Contract(abi);
    const arguments = JSON.parse(document.querySelector('#arguments').value);
    const data = contract.methods[method](...arguments).encodeABI();
    document.querySelector('#result').innerText = data;
  }
</script>
<style>
  textarea {
    width: 100%;
    height: 100px;
  }
</style>
<h1>Encode ABI Online</h1>
ABI <textarea id="abi" placeholder='[{"constant":false,"inputs":[{"name":"_required","type":"uint256"}],"name":"changeRequirement","outputs":[],"payable":false,"type":"function"}]'></textarea>
<br>
Method <input id="method" placeholder='changeRequirement'/>
<br>
Arguments <textarea id="arguments" placeholder='[1]'></textarea>
<br>
<button onclick="encodeABI()">Encode</button>
<pre id="result"></pre>