Syntax & Variables
14 min
Modern JavaScript variables are declared with const (can't be
reassigned) or let (can) — var still exists but is legacy, avoid it
in new code. Destructuring pulls values out of objects (const { name, age } = user) or arrays (const [first, second] = list) in one
step instead of repeated .property/[index] access. Template
literals (backtick strings) embed expressions directly with
${...}, instead of string concatenation with +.
const user = { name: "Ada", age: 30 };
const { name, age } = user;
console.log(`${name} is ${age} years old`);
// Ada is 30 years old
Destructuring works the same way for objects (by key) and arrays (by position) — both just unpack a structure into named variables in one line instead of several.
Write `formatUser(user)` — `user` is an object `{ name, age }`. Destructure it and return the string `"<name> is <age> years old"` using a template literal.
What's the difference between `const` and `let`?
You can destructure objects and arrays, and build strings with template literals instead of concatenation.