Objects are stored by reference, not value:
let obj1 = { name: "Alice" }
let obj2 = obj1 // Both point to same object
obj2.name = "Bob"
console.log(obj1.name) // "Bob" (changed!)
// Comparison checks reference
let a = { x: 1 }
let b = { x: 1 }
console.log(a === b) // false (different objects)
Assignment copies the reference, not the object. Changes through one variable affect all references.