Provide method for setting error state

[Garbee]

Action: Add method to textfield component to allow developers to set an error state and message.

[Sparticuz]

You can use the following to force an input into an invalid state programmatically.

document.getElementById('input-field').parentElement.className += ' is-invalid';
document.getElementById('input-error').textContent = 'Error Message';

[Sparticuz]

Actually, because the error and the input field are siblings, you could use

var ele = document.getElementById('input-error');
ele.parentElement.className += ' is-invalid';
ele.textContent = 'Error Message';

[traviskaufman]

Closing this; superseded by #4479 . This seems like something we'd probably want to carry over to our v2 implementation.