Mixins for Checkout estimation.js file Magento 2.

We can create mixins for Magento_Checkout/js/view/estimation file to modify the core Javascript method or add a new method to the file.

To create mixins, first, create a requirejs-config.js file in the module view/frontend area.

FilePath:
app/code/Jesadiya/Estimation/view/frontend/requirejs-config.js

Create Mixins js file to modify the core module’s original file with our changes,
app/code/Jesadiya/Estimation/view/frontend/web/js/view/estimation-mixin.js

You can add your custom logic before show sidebar with mixins,

Using the above way you can also modify other functions of estimation.js in the checkout module.