Modern Variables and Objects: let, const, and Destructuring

let count = 0;      // reassignable, block-scoped
const MAX = 100;     // NOT reassignable, block-scoped
var oldStyle = 'x';  // function-scoped — avoid in modern code

let and const are block-scoped — confined to the nearest { }, unlike the older var, which is function-scoped and a real source of bugs inside loops and conditionals. Default to const; only reach for let when a variable genuinely needs to be reassigned later.

const record = { name: 'Acme' };
record.name = 'Globomantics'; // allowed — the object's contents can change
record = {};                   // NOT allowed — reassigning the variable itself fails

const only prevents the variable from being reassigned to point at something else — it does not freeze the object's internal properties. This distinction matters a lot once Module 3's reactivity and Lesson 7's immutability patterns come into play.

// Object destructuring — pulling specific properties out
const { data, error } = wireResult;

// Array destructuring — pulling items by position
const [first, second] = accountList;

Destructuring is used constantly in LWC — most commonly to pull data and error out of a @wire result, a pattern Module 6 relies on directly.

LWC class fields and Apex/wire responses are almost always objects. Destructuring lets you extract exactly what you need in one clean line, instead of repeatedly writing wireResult.data, wireResult.error throughout a method.