tabbable.js

let tabbables;

function setTabbable(e) {
	if (e.keyCode === 9) {
		e.preventDefault();

		// the tabbable elements can be changed.
		tabbables = Array.prototype.slice.call(tabbable(this.currentStepView));

		const isFocused = tabbables.some((item, i) => {
			if (e.target === item) {

				if (i === tabbables.length - 1) {
					tabbables[e.shiftKey ? i - 1 : 0].focus();
				} else if (i === 0) {
					tabbables[e.shiftKey ? 0 : 1].focus();
				} else {
					tabbables[i + (e.shiftKey ? -1 : 1)].focus();
				}
				return true;
			}
			return false;
		});

		if (!isFocused) {
			tabbables[0].focus();
		}
	}
}