References

This chapter is a quick-reference guide to JavaScript’s core types, operators, built-in objects, and methods. Use it as a cheat sheet when writing code or preparing for interviews.

Core Data Types

Operators Reference

Class Syntax Reference

class Animal {
  constructor(name) { this.name = name; }
  speak() { console.log(`${this.name} makes a sound.`); }
  static classify() { return 'Mammal'; }
}

class Dog extends Animal {
  constructor(name, breed) {
    super(name);
    this.breed = breed;
  }
  speak() { console.log(`${this.name} barks.`); }
}

Array Methods

// Iteration
arr.forEach(fn); arr.map(fn); arr.filter(fn); arr.reduce(fn, init); arr.some(fn); arr.every(fn);

// Mutation
arr.push(v); arr.pop(); arr.shift(); arr.unshift(v); arr.splice(i, n); arr.sort(fn); arr.reverse();

// Access / search
arr.concat(arr2); arr.slice(i, j); arr.indexOf(v); arr.find(fn); arr.findIndex(fn); arr.flat(depth);

// Static
Array.from(iterable); Array.of(v1, v2, ...); Array.isArray(v);

String Methods

"hello".toUpperCase(); "HELLO".toLowerCase();
"hello".trim(); "hello".charAt(0); "hello".indexOf("e");
"hello".slice(1, 4); "hello".split(""); "hello".includes("ell");
"hello".startsWith("he"); "hello".endsWith("lo");
"hello".replace("l", "x"); "hello".repeat(3);
"a,b,c".split(","); "hello".padStart(10, "*");

Number & Math Methods

Number.isNaN(v); Number.isInteger(v); Number.parseFloat("3.14"); Number.parseInt("42", 10);
Number(v).toFixed(2);
Math.round(3.7); Math.floor(3.7); Math.ceil(3.2);
Math.min(1, 5, 3); Math.max(1, 5, 3);
Math.random(); // 0 to < 1
Math.abs(-5); Math.pow(2, 3); Math.sqrt(16); Math.PI;

Date Methods

const d = new Date();
d.getFullYear(); d.getMonth(); d.getDate(); d.getDay();
d.getHours(); d.getMinutes(); d.getSeconds();
d.toISOString(); d.toLocaleDateString(); d.toLocaleTimeString();
// Setting
d.setFullYear(2025); d.setMonth(11); d.setDate(25);
// Timestamp
Date.now(); d.getTime();

Browser Compatibility

All examples in this tutorial target modern browsers (Chrome, Firefox, Safari, Edge). For older browser support, use caniuse.com to check feature availability and consider transpilers like Babel and polyfills like core-js.