In pursuit of a real-world application, let's say we need an e-commerce web application for a mail-order coffee bean company. They sell several types of coffee and in different quantities, both of which affect the price.
First, let's go with the procedural route. To keep this demonstration down to earth, we'll have to create objects that hold the data. This allows the ability to fetch the values from a database if we need to. But for now, we'll assume they're statically defined:
// create some objects to store the data.
var columbian = {
name: 'columbian',
basePrice: 5
};
var frenchRoast = {
name: 'french roast',
basePrice: 8
};
var decaf = {
name: 'decaf',
basePrice: 6
};
// we'll use a helper function to calculate the cost
// according to the size and print it to an HTML list
function printPrice(coffee, size) {
if (size == 'small') {
var price = coffee.basePrice + 2;
}
else if (size == 'medium') {
var price = coffee.basePrice + 4;
}
else {
var price = coffee.basePrice + 6;
}
// create the new html list item
var node = document.createElement("li");
var label = coffee.name + ' ' + size;
var textnode = document.createTextNode(label+' price: $'+price);
node.appendChild(textnode);
document.getElementById('products').appendChild(node);
}
// now all we need to do is call the printPrice function
// for every single combination of coffee type and size
printPrice(columbian, 'small'),
printPrice(columbian, 'medium'),
printPrice(columbian, 'large'),
printPrice(frenchRoast, 'small'),
printPrice(frenchRoast, 'medium'),
printPrice(frenchRoast, 'large'),
printPrice(decaf, 'small'),
printPrice(decaf, 'medium'),
printPrice(decaf, 'large'),Tip
Downloading the example code
You can download example code files for all Packt books you have purchased from your account at http://www.packtpub.com. If you purchased this book elsewhere, you can visit http://www.packtpub.com/support and register to have the files e-mailed directly to you.
As you can see, this code is very basic. What if there were many more coffee styles than just the three we have here? What if there were 20? 50? What if, in addition to size, there were organic and non-organic options. That could increase the lines of code extremely quickly!
Using this method, we are telling the machine what to print for each coffee type and for each size. This is fundamentally what is wrong with imperative code.