Launch iOS keyboard

HTML

<button id="openKeyboard">Open Keyboard</button>
<input id="hiddenInput" style="visibility: hidden;">

JavaScript

document.getElementById('openKeyboard').addEventListener('click', function(){
        var inputElement = document.getElementById('hiddenInput');
        inputElement.style.visibility = 'visible'; // unhide the input
        inputElement.focus(); // focus on it so keyboard pops
        inputElement.style.visibility = 'hidden'; // hide it again
});