<button type="submit" id="button_next" data-bind="enable: isDisabled , text: getValue()" ></button>

/*global define*/
define(
    ['ko',
        'jquery',
        'Magento_Checkout/js/view/summary/abstract-total',
        'Magento_Checkout/js/model/quote',
        'Magento_Checkout/js/model/step-navigator',
        'mage/validation',
        'mage/translate'
    ],
    function (ko,$,Component, quote,stepNavigator) {
        "use strict";
        return Component.extend({
            defaults: {
                template: 'Magento_Checkout/button_next'
            },
            initialize: function () {
                this._super();
                return this;
            },
            initObservable: function () {
                console.log("INIT OBSERVABLE");
                this._super();

                this.isDisabled = function() {
                    //@TODO, check is not ok.
                    console.log("********************* IS DISABLED ?? *********************");
                    return true;
                }
                ;
                return this;
            },
            nextAction : function(){
               //@TODO
            },
            getPureValue: function() {
                var totals = quote.getTotals()();
                if (totals) {
                    return totals.grand_total;
                }
                return quote.grand_total;
            },
            getValue: function() {
                console.log('GET VALUE BUTTON NEXT');

                if(stepNavigator.getActiveItemIndex() == 0)
                    return $.mage.__('#BUTTON_NEXT#StepShipping');
                var price = this.getPureValue();
                if(price <= 0)  {
                    return $.mage.__('Free');
                }
                return $.mage.__('#BUTTON_NEXT#StepBilling') +' '+this.getFormattedPrice(price);
            }
        });
    }
);