Jan 26, 2026

Lecture Notes

Slides: JavaScript

Variables & Types

• JavaScript uses dynamic typing - variables adopt the type of their current value
• let declares reassignable variables, const declares immutable references
• Basic types: Numbers, Strings, Booleans, Arrays, Objects
• Type coercion automatically converts types during operations (e.g., '40' - 2 = 38)
• Use === for strict equality (no type coercion), == allows coercion

Truthy & Falsy Values

• Falsy values: false, 0, '' (empty string), null, undefined, NaN
• Everything else is truthy (including empty arrays and objects)
• undefined in conditionals evaluates to false

Arrays

• Declared using literal syntax: const arr = ['a', 'b', 'c']
• Zero-indexed access: arr[0] returns first element
• Out-of-bounds access returns undefined
• Can mix types: ['dogs', 2.5, true, [3,4,0]]
• .length property returns array size
• .push(value) adds element to end
• Nested arrays for multi-dimensional data: arr[2][0]

Objects

• Unordered key-value pairs (like dictionaries/maps)
• Declared as: const obj = {key: 'value', name: 'Alice'}
• Access via bracket notation: obj['key'] or dot notation: obj.key
• Bracket notation required for variables: obj[variableName]
• Objects can be nested: person.favorites.food

Data Tables

• Arrays of objects represent tabular data (like spreadsheets)
• Each object is a row, each key is a column
• Example: [{name: 'Ada', age: 30}, {name: 'Bob', age: 25}]

Control Flow

• If/else syntax similar to Java
• for loops: traditional index-based or for...of for arrays
• for...in iterates through object keys

Functions

• Declared with: function name(params) { return value; }
• No access modifiers or explicit return types
• Parameters don't specify types