Are objects passed by reference?

Understand the concept

JavaScript passes every argument by value. For an object, the copied value is a reference to that object, so the caller and function can still reach the same underlying object. This explains why changing a property affects the caller, but assigning a new object to the parameter does not.

Important ideas

• JavaScript passes values; for an object, that value is a reference.

• Changing a shared object's property affects the original object.

• Reassigning a function parameter does not reassign the caller's variable.

• Primitive values such as numbers and strings do not share mutable object contents.

• Arrays and functions are objects too, so the same reference behavior applies to them.

Work through the example

function update(user) {
  user.name = 'Neha';
  user = { name: 'Ravi' };
}
const original = { name: 'Asha' };
update(original);
console.log(original.name); // Neha

• The property change affects the shared object; reassigning the parameter only changes that local binding.