Swizec Teller - a geek with a hatswizec.com

    Finally, a practical use case for JavaScript generators!

    JavaScript generators are amazing. A brilliant concept infinitely useful on paper.

    They let you write infinite loops that terminate. Yield values from functions before they finish. Build lazy data structures. Lazy evaluation programming!

    A functional programmer's wet dream. 😍

    And I bet you've never used a JavaScript generator even once did you? Do you even know the syntax?

    I bet you don't.

    Turns out generators aren't very useful in practice. 😒

    But yesterday, after years of knowing about generators, years of itching to use them, years of ... I FOUND A USE! A real world practical use-case where generators actually make your code better. 😱

    We were adding automatic linking of twitter usernames to my TechLetterApp project. Find a piece of text, parse out @username instances, turn into links.

    Easy right?

    I thought so too. Complications around inserting complex nodes into an abstract syntax tree (AST) aside, parsing those usernames is hard to do elegantly.

    Unless you use generators πŸ˜›

    Here's how we did it πŸ‘‡

    First, you create a regex that matches @ followed by a series of word symbols.

    const UserRegex = new RegExp(/@(\w+)/, "g");

    Then you create a generator that runs this regex in a loop. Each UserRegex.exec() returns the next match.

    function* getUsernames(string) {
    let match = null;
    do {
    match = UserRegex.exec(string);
    if (match) {
    yield match;
    }
    } while (match);
    }

    We have a *getUsernames generator that takes a string. The asterisk notation changes a function to a generator.

    Inside, a loop runs as long as match has a value. Assigned on each iteration as a UserRegex.exec call.

    We yield existing values on every loop iteration. Last one will be null and we don't want to return those.

    Yield is how you return values from generators. Notice that even after returning a value, the generator keeps running. That's the generator magic πŸ§™β€β™€οΈ

    You can now find all usernames in a string with a loop.

    const string = "this is a test with @swizec and @kyleshevlin, maybe @lukeed05"
    for (const username of getUsernames(string)) {
    console.log(username)
    }

    That outputs

    ["@swizec", "swizec"]
    ["@kyleshevlin", "kyleshevlin"]
    ["@lukeed05", "lukeed05"]

    Here's a CodeSandbox you can play with

    Cheers, ~Swizec

    Did you enjoy this article?

    Published on April 17th, 2019 in Frontend Web, Livecoding, Technical

    Learned something new?
    Want to become an expert?

    Here's how it works πŸ‘‡

    Leave your email and I'll send you thoughtfully written emails every week about React, JavaScript, and your career. Lessons learned over 20 years in the industry working with companies ranging from tiny startups to Fortune5 behemoths.

    Join Swizec's Newsletter

    And get thoughtful letters πŸ’Œ on mindsets, tactics, and technical skills for your career. Real lessons from building production software. No bullshit.

    "Man, love your simple writing! Yours is the only newsletter I open and only blog that I give a fuck to read & scroll till the end. And wow always take away lessons with me. Inspiring! And very relatable. πŸ‘Œ"

    ~ Ashish Kumar

    Join over 10,000 engineers just like you already improving their careers with my letters, workshops, courses, and talks. ✌️

    Have a burning question that you think I can answer?Β I don't have all of the answers, but I have some! Hit me up on twitter or book a 30min ama for in-depth help.

    Ready to Stop copy pasting D3 examples and create data visualizations of your own? Β Learn how to build scalable dataviz components your whole team can understand with React for Data Visualization

    Curious about Serverless and the modern backend? Check out Serverless Handbook, modern backend for the frontend engineer.

    Ready to learn how it all fits together and build a modern webapp from scratch? Learn how to launch a webapp and make your first πŸ’° on the side with ServerlessReact.Dev

    Want to brush up on your modern JavaScript syntax?Β Check out my interactive cheatsheet: es6cheatsheet.com

    By the way, just in case no one has told you it yet today: I love and appreciate you for who you are ❀️

    Created bySwizecwith ❀️