Magento – Failed to load the “Magento_Checkout/js/view/cart/totals” component

From my understanding, to set the observable the way Magento uses knockout you would have to create an initialize function starting with this._super(); which will allow to call the parents.

define(
[   
'ko',
'jquery',
'Magento_Checkout/js/view/summary/shipping',
'Magento_Checkout/js/model/quote',
'Magento_Checkout/js/model/step-navigator'
],
function (ko, $, Component, quote, stepNavigator ) {
    var displayMode = window.checkoutConfig.reviewShippingDisplayMode;

    return Component.extend({
        defaults: {
            displayMode: displayMode,
            template: 'Magento_Tax/checkout/summary/shipping'
        },

        initialize: function () {
            this._super();

            this.newVar = ko.observable(this.getValue());
        },


        ...


    });
}
);

You should then be able to call the parents from anywhere in the code after the initialize function.

Also data-bind should be:

<span data-bind="text: newVar"></span>

Useful tips for using this:

If the need comes to access this from inside computed observables or keeping track of it using function overriding the this variable, you may simply use the appoach below.

self = this;
self.firstName = ko.observable('Some');
self.lastName = ko.observable('One');
self.fullName = ko.computed(function() {
    return self.firstName() + " " + self.lastName();
});

To pass this or any variable inside of a computed observable:

this.fullName = ko.computed(function() {
    return this.firstName() + " " + this.lastName();
}, this); //PASSED VARIABLE

if that's still relevant, here's the answer:

Magento_SalesRule/js/view/payment/discount requires Magento_Checkout/js/model/quote, which asks for window.checkoutConfig.quoteData on line 32:

quoteData = window.checkoutConfig.quoteData,

window.checkoutConfig is not available anywhere except the checkout page - it is set in module-checkout/.../templates/onepage.phtml on line 26:

window.checkoutConfig = <?= /* @escapeNotVerified */ $block->getSerializedCheckoutConfig() ?>;

So, you are getting a TypeError: Cannot read property 'quoteData' of undefined. After that, url-builder produces the same kind of error when trying to read window.checkoutConfig.storeCode. You can see it if you set a breakpoint in require.js on line 883, where it handles such errors. Look at the stack trace printed in the console and click on the function call right before onError (it says check).