JavaScript Data Types

JavaScript is a dynamically typed language, but it still has a robust set of data types that you must master.

1. Primitives (Stored by Value)

• String: "Hello World"
• Number: 42, 3.14 (There is no separate integer vs double).
• Boolean: true or false.
• Undefined: A variable that has been declared but not assigned a value.
• Null: An empty value. (Note: typeof null === 'object' - a famous JS bug).
• Symbol: Unique and immutable values (ES6).
• BigInt: For integers larger than $2^53 - 1$.

2. Objects (Stored by Reference)

• Object: A collection of properties ({ key: value }).
• Array: An ordered list of values ([1, 2, 3]).
• Function: A callable object.
• Date: For handling dates and times.

Reference Axiom:

When you copy a primitive, you create a new value. When you copy an object, you create a new reference to the same object in memory.

const obj1 = { name: 'A' };
const obj2 = obj1;
obj2.name = 'B';
console.log(obj1.name); // 'B' (Changes affect both)

Next Step: Mastering Complex Syntax.types, type coercion, and memory allocation.