How to extend js class/method of checkout model class in magento 2

Question

Basically I need to some method overwrite/extend of following Js class.

magento/module-checkout/view/frontend/web/js/model/step-navigator.js

Overwrite of this class through requirejs working fine. But I need to extend one of method of this class. here is an example of overwrite requirejs-config.js

var config = {
    "map": {
        "*": {
            "Magento_Checkout/js/model/step-navigator": "SR_Checkout/js/model/step-navigator"
        }
    }
};

How to extend some method of any model class in checkout.

Answer 1

You need create requirejs-config.js in you module with

var config = {
    config: {
        mixins: {
            'Magento_Checkout/js/model/step-navigator': {
                'You_Module/js/step-navigator/pluggin': true
            }
        }
    }
};

And js/step-navigator/pluggin.js file with content like

define(function () {
    'use strict';

    return function (target) { // target == Result that 'Magento_Checkout/js/model/step-navigator' returns.
        // modify target
        var navigateTo = target.navigateTo;
        target.navigateTo = function(code, scrollToElementId) {
            if (code == ...) { // before  method
              ....
            }
            var result = navigateTo.apply(this, arguments);
            //after method call
            return  result;
        };
        return target.
    };
});

Answer 2

This still works in 2.2.7. Thank you very much KAndy. You can also add veriables if you want to change it like this:

var result = navigateTo.apply(this, [code, scrollToElementId]);
        //after method call