TypeScript Project: Library Catalog

What you will build

A catalog is an array of books. Each book has a title, an author, and a year. You print the full shelf, then search by author and list every match. Search uses includes so a last name can match inside a longer author field.

The shelf is hardcoded. Compile with Try it in TypeScript at/typescript/try. This is TypeScript, not a Python script and not a C++ file.

A Book interface

Three fields travel together. Title and author are strings. Year is a number. Printing one book is a single function so the catalog loop stays short.

interface Book {
  title: string;
  author: string;
  year: number;
}

function printBook(b: Book): void {
  console.log(b.title + " - " + b.author + " (" + b.year + ")");
}

const b: Book = {
  title: "Programming TypeScript",
  author: "Boris Cherny",
  year: 2019,
};
printBook(b);

Fill a catalog

Book[] grows with push. A for...of loop prints every row. Pass the catalog into the print helper.

interface Book {
  title: string;
  author: string;
  year: number;
}

function printBook(b: Book): void {
  console.log(b.title + " - " + b.author + " (" + b.year + ")");
}

function printCatalog(shelf: Book[]): void {
  console.log("Catalog (" + shelf.length + " books)");
  for (const b of shelf) {
    printBook(b);
  }
}

const shelf: Book[] = [];
shelf.push({ title: "Programming TypeScript", author: "Boris Cherny", year: 2019 });
shelf.push({ title: "Effective TypeScript", author: "Dan Vanderkam", year: 2019 });
shelf.push({ title: "TypeScript Cookbook", author: "Stefan Baumgartner", year: 2023 });
printCatalog(shelf);

Search with includes

author.includes(query) is true when the query is a substring. A query of Chernymatches Boris Cherny. An empty query matching every book is possible with includes; this project treats an empty query as no hits so a blank search does not dump the shelf.

const author: string = "Boris Cherny";
const query: string = "Cherny";
if (author.includes(query)) {
  console.log("match");
} else {
  console.log("no match");
}

Complete catalog program

Walk the array. When the author field contains the query, print that book and count it. After the loop, print how many matches you found. Two searches run at the bottom of the file: one that hits twice, one that hits none.

interface Book {
  title: string;
  author: string;
  year: number;
}

function printBook(b: Book): void {
  console.log(b.title + " - " + b.author + " (" + b.year + ")");
}

function searchByAuthor(shelf: Book[], query: string): void {
  console.log("Search author: " + query);
  if (query.length === 0) {
    console.log("Empty query, 0 matches");
    return;
  }
  let hits = 0;
  for (const b of shelf) {
    if (b.author.includes(query)) {
      printBook(b);
      hits = hits + 1;
    }
  }
  console.log(hits + " match(es)");
}

const shelf: Book[] = [];
shelf.push({ title: "Programming TypeScript", author: "Boris Cherny", year: 2019 });
shelf.push({ title: "Effective TypeScript", author: "Dan Vanderkam", year: 2019 });
shelf.push({ title: "Learning TypeScript", author: "Josh Goldberg", year: 2022 });
shelf.push({ title: "TypeScript in 50 Lessons", author: "Stefan Baumgartner", year: 2020 });
shelf.push({ title: "TypeScript Cookbook", author: "Stefan Baumgartner", year: 2023 });

console.log("All books");
for (const b of shelf) {
  printBook(b);
}
console.log("");
searchByAuthor(shelf, "Baumgartner");
console.log("");
searchByAuthor(shelf, "Ada");

The Baumgartner search prints two titles and 2 match(es). The Ada search prints0 match(es). Search is case-sensitive: baumgartner would miss these rows.

Common mistakes

• Comparing authors with === only. Then Baumgartner fails againstStefan Baumgartner. Use includes when you want a substring.
• Using indexOf and testing against 0. A match at the start of the string is index 0, which is a hit. The miss value is -1, or skip the index and use includes.
• Forgetting to count hits. Printing books without a total makes an empty result look like a crashed loop.
• Storing year as a string. Numeric year lets you add a filter such as “after 2020” later without parsing.

Practice

1. Change the Ada search query to Goldberg and confirm one match prints.
2. Add a sixth book by Dan Vanderkam and confirm that author search now lists two titles.
3. Add a search-by-title function that also uses includes, and print only books with year >= 2022.

Next project: convert Celsius, Fahrenheit, and Kelvin with formatted output.