when I pass a variable as a function parameter, is a new copy of the variable value or a memory reference javascript

When I pass a variable as a function parameter, is a new copy of the variable value or a memory reference in JavaScript?

When you pass a variable as a function parameter in JavaScript, it depends on the variable type whether it is passed as a copy of the value or a reference to the memory location.

Primitive Data Types:

Primitive data types (such as numbers, strings, and booleans) are passed as a copy of the value.

let num = 5;

function changeNum(num) {
  num = 10;
}

changeNum(num);

console.log(num); // Output: 5

In the above example, the original value of num is not changed because the changeNum function creates a new copy of the num variable inside its scope. Even though this copy has the same name, it has a different memory location than the original num variable.

Reference Data Types:

Reference data types (such as objects and arrays) are passed as a reference to the memory location.

let arr = [1, 2, 3];

function addItem(array) {
  array.push(4);
}

addItem(arr);

console.log(arr); // Output: [1, 2, 3, 4]

In the above example, the original arr value is changed because the addItem function receives a reference to the memory location of the arr variable. This means that any changes made to the array inside the function will affect the original array as well.

Passing Objects by Value:

It is possible to pass an object as a copy of its value by creating a new object inside the function and copying the properties of the original object to the new object.

let obj = { name: "John", age: 30 };

function changeName(newObj) {
  newObj.name = "Jane";
}

changeName(Object.assign({}, obj));

console.log(obj.name); // Output: John

In the above example, a new object is created using the Object.assign() method and passed to the changeName function. This method creates a shallow copy of the obj object, and any changes made to the new object will not affect the original object.

Overall, it is important to understand whether a variable is passed by value or by reference when working with functions in JavaScript, as it can affect how changes made inside a function affect the original variable.