Working with Data

JavaScript provides built-in types and objects for working with strings, numbers, dates, and more. Mastering these is essential for real-world development.

Strings

Strings represent text and are enclosed in single quotes, double quotes, or backticks.

let single = 'Hello';
let double = "World";
let template = `Hello, ${single}!`; // Template literal with interpolation

String Methods

let str = "JavaScript is awesome";

console.log(str.length);            // 21
console.log(str.toUpperCase());     // "JAVASCRIPT IS AWESOME"
console.log(str.toLowerCase());     // "javascript is awesome"
console.log(str.indexOf("is"));     // 11
console.log(str.slice(0, 10));      // "JavaScript"
console.log(str.includes("awesome")); // true
console.log(str.split(" "));        // ["JavaScript", "is", "awesome"]
console.log(str.replace("awesome", "fun")); // "JavaScript is fun"

Template Literals

Template literals (backticks) allow embedded expressions and multi-line strings:

let name = "Bob";
let age = 30;
let greeting = `Hi, I'm ${name} and I'm ${age} years old.`;

let multiLine = `
  This is
  a multi-line
  string
`;

Numbers

JavaScript has a single Number type for both integers and floating-point numbers.

let integer = 42;
let float = 3.14;
let negative = -10;

// Parsing strings to numbers
console.log(parseInt("42px"));    // 42
console.log(parseFloat("3.14em")); // 3.14

// Formatting
let num = 123.456;
console.log(num.toFixed(2));      // "123.46"
console.log(num.toPrecision(4));  // "123.5"

// Special values
console.log(Infinity);            // Infinity
console.log(NaN);                 // NaN (Not a Number)
console.log(isNaN("hello"));      // true

Dates

The Date object handles dates and times:

let now = new Date();
let specific = new Date(2025, 0, 15); // Jan 15, 2025 (months are 0-indexed)
let fromString = new Date("2025-01-15");

console.log(now.getFullYear());
console.log(now.getMonth());      // 0—11
console.log(now.getDate());
console.log(now.getDay());        // 0 (Sunday) — 6
console.log(now.toLocaleDateString("en-US"));
console.log(now.toISOString());

Temporal API (Modern Alternative)

The Temporal API is a modern replacement for the Date object, providing immutable date/time types:

// Temporal is available in modern environments
// const today = Temporal.Now.plainDateISO();
// const dueDate = today.add({ days: 7 });

Math Object

console.log(Math.PI);           // 3.141592653589793
console.log(Math.round(4.7));   // 5
console.log(Math.floor(4.7));   // 4
console.log(Math.ceil(4.3));    // 5
console.log(Math.random());     // Random number between 0 and 1
console.log(Math.max(1, 5, 3)); // 5
console.log(Math.min(1, 5, 3)); // 1

Regular Expressions

RegExp is used for pattern matching in strings:

let pattern = /hello/i; // Case-insensitive
let text = "Hello World";

console.log(pattern.test(text));       // true
console.log(text.match(pattern));      // ["Hello"]
console.log(text.replace(/world/i, "JS")); // "Hello JS"

Type Conversion

// Implicit conversion
console.log("5" + 3);   // "53" (string concatenation)
console.log("5" - 3);   // 2 (numeric subtraction)

// Explicit conversion
console.log(Number("42"));    // 42
console.log(String(42));      // "42"
console.log(Boolean(0));      // false
console.log(Boolean(""));     // false
console.log(Boolean("text")); // true