4 Extracting calculations from actions
In this chapter
- Observe how information enters and leaves a function.
- Discover functional techniques to make code more testable and reusable.
- Learn how to extract calculations from actions.
In this chapter, we’re going to do a lot of refactoring. We’re going to look at an existing piece of software, add some features, and then refactor calculations out of the actions. This improves the reuse and testability of the code.
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var shopping_cart = []; #1 var shopping_cart_total = 0; function add_item_to_cart(name, price) { shopping_cart.push({ #2 name: name, price: price }); calc_cart_total(); #3 } function calc_cart_total() { shopping_cart_total = 0; for(var i = 0; i < shopping_cart.length; i++) { var item = shopping_cart[i]; #4 shopping_cart_total += item.price; } set_cart_total_dom(); #5 }
The final line updates the document object model (DOM), which is how web programmers modify a web page in the browser.
Vocab time
The document object model (DOM) is the in-memory representation of an HTML page in a browser.
Calculating free shipping
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