A snippet that can be added to stock Impulse themes to give AJAX functionality to the /cart page. This is basically a public API, exposing cartPage methods and variables to work with in other JS files

ajax-cart-page.js

/**
 * simply add this file to theme.liquid in order to have the /cart page update
 * using ajax. the only dependency is theme.jQuery
 */

window.cartPage = window.cartPage || {};

(function($){
  var $ = jQuery = $;

  cartPage.selectors = {
    cartForm: 'form.cart',
    qtyButtons: '.cart__product-qty',
    mainContent: '#MainContent',
    removeButtons: 'a.btn',
    subtotal: 'form.cart .cart__row:last-child .cart__row--table',
    updateButton: '.cart__update',
  };

  // cache DOM
  var $cartForm = $(cartPage.selectors.cartForm),
      $document = $(document);

  /*==========================================================================
    Utilities
  ============================================================================*/
  cartPage.utils = {
    getCurrentRow: function(elem) {
      var $parentRow = $(elem).closest('.cart__row')[0];

      // this is the current .cart__row's index, plus 1 so we can use it with
      // css nth-child selector
      return $('.cart__row').index($parentRow) + 1;
    },

    removeRow: function(rowNumber) {
      $('form.cart .cart__row:nth-child(' + rowNumber + ')').remove();
    },
  };

  /*==========================================================================
    Theme Functionality
  ============================================================================*/
  cartPage.init = function() {
    cartPage.hideUpdateButton();
    cartPage.bindEvents();
  }

  cartPage.bindEvents = function() {
    // quantity change
    $document.on('blur', cartPage.selectors.qtyButtons, function() {
      var formData = $cartForm.serialize(),
          currentRow = cartPage.utils.getCurrentRow(this),
          quantity = this.value;

      $.post($cartForm.attr('action'), formData, function(data) {
        // reload the current line item's quantity and pricing
        cartPage.reloadNode('form.cart .cart__row:nth-child(' + currentRow + ') > .cart__row--table-large > .grid__item:last-child');

        if (quantity <= 0) {
          // remove the current row
          cartPage.utils.removeRow(currentRow);
        }

        // reload the subtotal
        cartPage.reloadNode(cartPage.selectors.subtotal);
      });
    });

    // product remove
    $document.on('click', cartPage.selectors.removeButtons, function(e) {
      e.preventDefault();

      var currentRow = cartPage.utils.getCurrentRow(this);

      $.post(this.href, function() {

        // remove the current row
        cartPage.utils.removeRow(currentRow);

        // reload the subtotal
        cartPage.reloadNode(cartPage.selectors.subtotal);
      });
    });
  }

  cartPage.reloadNode = function(selector, callback) {
    // refill selector with it's children
    $(selector).load(document.URL +  ' ' + selector + ' > *', function() {
      if (!!callback) {
        callback();
      }
    });
  }

  cartPage.hideUpdateButton = function() {
    // using style element so that reloading form does not affect hidden state
    var style = document.createElement('style');
    style.type = 'text/css';
    style.innerHTML = cartPage.selectors.updateButton + '{display:none;}';
    document.getElementsByTagName('head')[0].appendChild(style);
  }

  /*==========================================================================
    Initialize
  ============================================================================*/
  if ( window.location.pathname.indexOf('cart') > -1 ) {
    cartPage.init();
  }

})(theme.jQuery);