JavaScript Tutorial
Data types define how values behave in memory and operations. Strong type awareness prevents runtime errors and logical bugs.
Why this matters
Type confusion causes common issues like incorrect comparisons, unexpected coercion, and method errors.
JavaScript primitives include string, number, bigint, boolean, undefined, null, and symbol.
Primitives are immutable values. Operations create new values rather than changing original primitive data.
typeof helps with quick checks, but note that typeof null returns object due to historical behavior.
Objects, arrays, and functions are reference types. Assignment copies the reference, not deep content.
Mutating through one reference affects all references pointing to same object.
Use spread or structuredClone for safer copy patterns when immutability is needed.
const user = "Asha";
const score = 91;
const active = true;
let note;
const nothing = null;
console.log(typeof user); // string
console.log(typeof score); // number
console.log(typeof active); // boolean
console.log(typeof note); // undefined
console.log(typeof nothing); // object (legacy behavior)Use type checks before method calls for safer code.
const a = { theme: "light" };
const b = a;
b.theme = "dark";
console.log(a.theme); // darkBoth variables point to same object in memory.
const original = { name: "Ravi", city: "Pune" };
const copied = { ...original };
copied.city = "Delhi";
console.log(original.city); // Pune
console.log(copied.city); // DelhiSpread creates a new top-level object reference.
Prefer strict equality (===) to avoid coercion surprises.
Handle them intentionally based on business logic.
Use copy patterns when independent objects are required.
Seven: string, number, bigint, boolean, undefined, null, and symbol.
It is a long-standing language quirk kept for backward compatibility.
Use structuredClone where available, or robust deep-copy strategies based on data structure.
Array is a reference type (object).