Code Explainers

Beginner code explainers

go 
package textutil
 
import "strings"
 

Extracting delimited text with strings.Cut

string-parsing delimiters standard-library
Beginner 7 steps
javascript 
const form = document.querySelector('#profile-form');
let isDirty = false;
 
form.addEventListener('input', () => {

Warn before leaving a form with unsaved edits

event-listeners dom state-tracking
Beginner 5 steps
typescript 
export function formatDuration(ms: number): string {
  if (!Number.isFinite(ms) || ms < 0) {
    return "00:00";
  }

Formatting milliseconds as a clock string

formatting integer-math guard-clause
Beginner 4 steps
php 
<?php
 
function timeAgo(DateTimeInterface $past, ?DateTimeInterface $now = null): string
{

Building a timeAgo helper in PHP

datetime formatting pluralization
Beginner 6 steps
ruby 
class OrderMailerPreview < ActionMailer::Preview
  def confirmation
    OrderMailer.confirmation(sample_order)
  end

Previewing Rails mailers with sample data

mailer-previews test-fixtures in-memory-objects
Beginner 6 steps
rust 
use base64::engine::general_purpose::{STANDARD, URL_SAFE_NO_PAD};
use base64::{DecodeError, Engine};
 
pub fn encode_standard(data: &[u8]) -> String {

Base64 encode and decode in Rust

base64 encoding error-handling
Beginner 7 steps
rust 
pub fn collapse_whitespace(input: &str) -> String {
    let mut result = String::with_capacity(input.len());
    let mut in_whitespace = false;
 

Collapsing runs of whitespace in Rust

string-processing state-machine iteration
Beginner 5 steps
python 
import wave
import os
from dataclasses import dataclass
 

Reading WAV metadata into a dataclass

dataclass audio file-io
Beginner 5 steps
rust 
use std::collections::HashSet;
use std::io::{self, BufRead, BufWriter, Write};
 
fn main() -> io::Result<()> {

Filtering duplicate lines in Rust

stdin hashset buffering
Beginner 5 steps
go 
package config
 
import (
	"fmt"

Loading typed config from environment variables in Go

configuration environment-variables type-parsing
Beginner 8 steps
javascript 
function validateSignup({ email, password, confirmPassword, username, age }) {
  const errors = {};
 
  if (!email) {

Building a signup validator in JavaScript

validation regex guard-clauses
Beginner 7 steps
java 
public class SortedListMerger {
 
    public static int[] merge(int[] a, int[] b) {
        int[] result = new int[a.length + b.length];

Merging two sorted arrays in Java

two-pointers merging arrays
Beginner 6 steps
java 
public final class RegistrationValidator {
 
    private static final Pattern EMAIL = Pattern.compile("^[\\w.+-]+@[\\w-]+\\.[\\w.-]+$");
    private static final Pattern USERNAME = Pattern.compile("^[a-zA-Z0-9_]{3,20}$");

Accumulating validation errors in Java

validation regex error-accumulation
Beginner 9 steps
php 
<?php
 
namespace App\Http\Middleware;
 

Enforcing a JSON Accept header in Laravel

middleware content-negotiation http-headers
Beginner 5 steps
go 
package handlers
 
import (
	"net/http"

Rendering HTML pages with Gin handlers

http-handlers templating error-handling
Beginner 8 steps
go 
package handlers
 
import (
	"net/http"

Reading path parameters in Gin

routing path-parameters wildcards
Beginner 7 steps
python 
from collections import Counter
 
 
def word_frequencies(text):

Counting things with collections.Counter

counting multiset data-structures
Beginner 8 steps
go 
package geometry
 
import "fmt"
 

Implementing fmt.Stringer in Go

interfaces stringer composition
Beginner 5 steps