Forem: JianTeng

Checking union types in Typescript

JianTeng — Wed, 28 Dec 2022 06:17:42 +0000

It is a common use case where we check for multiple strings matches in if statements, as shown in the example below.

const exampleMovement: string = '';

if (exampleMovement === 'up' || exampleMovement === 'down' || exampleMovement === 'left' || exampleMovement === 'right') {
    // application logic
}

We can clean it up by introducing an array and using the includes function.

if (['up', 'down', 'left', 'right'].includes(exampleMovement)) {
    // application logic
    // exampleMovement type is string
}

The downside is exampleMovement type is still string.

If we want to narrow the type, we can use a type predicates.

const movementTypeCheck = (movement:string): movement is 'up' | 'down' | 'left' | 'right' => {
    return ['up','down','left','right'].includes(movement);
}

if (movementTypeCheck(exampleMovement)) {
    // application logic
    // exampleMovement type is union of 'up','down','left','right'
}

Extract dynamic text using regex capturing group

JianTeng — Tue, 20 Dec 2022 02:11:06 +0000

We can quickly extract dynamic text using regex capturing group. It is useful when we want to extract information from a bunch of strings that are using the same words.

const example = 'You have bought 2 tickets'
const regex = /You have bought (?<tickets>\d*) tickets/
const match = example.match(regex);

console.log(match.groups.tickets);
// output: 2

In the example above, we want to extract the number of tickets from the string You have bought 2 tickets. We can define a regular expression pattern by enclosing it between slashes.

Next, we can define the named capturing group using (?<Name>x). We can access it in the match.groups object.

Here's an example where we extract multiple text.

const example = 'You have bought 2 tickets and 5 drinks'
const regex = /You have bought (?<tickets>\d*) tickets and (?<drinks>\d*) drinks/
const match = example.match(regex);

console.log(match.groups);
/*
output: { tickets: '2', drinks: '5' }
*/

3 Learnings from Advent of Code 2022

JianTeng — Fri, 16 Dec 2022 03:41:15 +0000

I came to know about Advent of Code from this YouTube video, and I have been enjoying it! My goal is just to be able to collect all 50 stars. Here are some of my learnings from it (I am not a competitive programmer).

1. Not giving up

As the difficulty of the problem varies, sometimes it's easy to get stuck. It is tempting to look for solutions on Reddit, but it is more satisfying solving the problem on your own. I would take a break and go do something else if I get stuck, and often times different ideas pop out as I re-approach the problem. My debugging skills definitely improved by not giving up!

2. Learning from others

At the end of the day, after solving the questions, I would look at how others have solved it. And often times, I am amazed by the different approaches! When I looked back at my naive solution, it looks comical. Day by day, I have been learning a ton.

I am looking at solution either from Reddit thread or GitHub topics.

3. Have fun!

I enjoyed solving problems for the Elves. Of course, the memes on Reddit always provide a good laugh.