What does it mean that functions are "first-class citizens" in JavaScript?

Functions are first-class citizens — they're treated as values just like strings or numbers. This means:

• Assign to variables
• Pass as arguments
• Return from functions
• Store in arrays/objects
• Have properties and methods attached

// Assigned to variable
const greet = (name) => 'Hello, ' + name;

// Passed as argument (callback)
[1, 2, 3].forEach(function(n) { console.log(n); });

// Returned from function
function makeAdder(x) {
  return (y) => x + y; // ← function as return value
}
const add5 = makeAdder(5);
add5(3); // 8

// Stored in object
const math = {
  add: (a, b) => a + b,
  sub: (a, b) => a - b,
};

// Has properties
function fn() {}
fn.version = '1.0';
console.log(fn.name);   // 'fn'
console.log(fn.length); // 0 (param count)