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Using TypeScript to create order summary.
/**
* Wed, 15 Nov 2017 at 0:56:13 MYT
* "Using TypeScript to create order summary."
*
* The purpose of this snippet is to demonstrate the
* use of TypeScript in our code.
* You can run this code online here:
* https://www.typescriptlang.org/play/
*
* PS:
* The code is based on Fun Fun Function (@mpjme),
* Unit testing in JavaScript Part 1
* https://www.youtube.com/watch?v=Eu35xM76kKY
*
**/
interface IOrderItem {
name: string;
price: number;
shipppingCost?: number; // TS: use `?` to indicate optional property
}
interface IOrder {
// [TRY THIS]
// using VSCode, hover on `IOrderItem` below
// and hold `option` key (OSX) to display symbol definition
items: Array<IOrderItem>;
}
interface IOrderSummary {
itemsCount: number;
totalPrice: number;
}
const orderSummary = (order: IOrder): IOrderSummary => {
const initialValue: number = 0; // ← [TRY THIS] change `number` to `string` and see the error
const totalPrice: number = order.items.reduce(
(prev: number, current: IOrderItem): number => {
// [CHALLENGE] convert this return statement into ES6 "Implicit Return Shorthand"
return prev + current.price + (current.shipppingCost || 0);
},
initialValue
);
return {
itemsCount: order.items.length,
totalPrice // ← use ES6 property-value shorthand
};
};
// [TRY THIS] change `IOrder` to other type and see the error
const sampleOrder: IOrder = {
items: [
{
name: "Penetration Tester's Open Source Toolkit",
price: 100,
shipppingCost: 21
},
{
name: "Gray Hat Hacking Second Edition",
price: 250
// notice that it's *safe* to not put `shippingCost` here
// because we declared it as optional in interface `IOrderItem`
}
]
};
const summary = orderSummary(sampleOrder);
// sample of test case
console.log(summary, summary.totalPrice == 371 ? "✔ PASSED" : "✘ FAILED");
console.log(summary, summary.totalPrice != 370 ? "✔ PASSED" : "✘ FAILED");
// ----------------------------
//
// Bonuses:
// 1. command to re-run this file on save:
// → `nodemon --watch '*.ts' --exec 'ts-node' orderSummary.ts`
// 2. Article about JS shorthand techniques:
// → https://www.sitepoint.com/shorthand-javascript-techniques/
//
// ----------------------------
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