inputhandler.js

var InputHandler = function InputHandler() {
        var inputs = document.querySelectorAll('input'),
            i = 0;

        for (i; i < inputs.length; i++) {
            inputs[i].addEventListener('focus', this.handleLabelState);
            inputs[i].addEventListener('blur', this.handleLabelState);
        }
    };

    InputHandler.prototype.handleLabelState = function(event) {
        var input = event.target,
            label = document.querySelector('label[for="' + input.getAttribute('id') + '"]');

        if (!label) {
            return false;
        }

        if (event.type === 'focus' || input.value) {
            label.classList.add('is-active');
        } else {
            label.classList.remove('is-active');
        }
    };

    new InputHandler();