Add Property at the Start of a Javascript Object

In JavaScript, objects are collections of key-value pairs where properties and methods can be added, modified, or deleted dynamically. If you want to add a property at the beginning of an existing object, you typically need to create a new object and then copy the existing properties along with the new property you want to add. Here’s how you can do it:

Example Scenario:#

Let’s say you have an existing object:

let person = {
  lastName: "Doe",
  age: 30,
};

And you want to add a new property firstName at the beginning of this object.

Approach:#

Create a new object: Start by creating a new object that includes the new property you want to add.
Copy existing properties: Iterate through the existing object and copy its properties to the new object.
Assign the new object to the existing variable: Replace the original object with the new object containing the added property.

Here’s how you can implement this:

let person = {
  lastName: "Doe",
  age: 30,
};

// Step 1: Create a new object with the new property
let updatedPerson = {
  firstName: "John", // New property added at the beginning
  ...person, // Spread operator to copy existing properties
};

// Step 2: Replace the original object with the updated object
person = updatedPerson;

console.log(person);

Explanation:#

Step 1: We create a new object updatedPerson and use the spread (...) operator to copy all properties from person into updatedPerson. We also add the firstName property at the beginning of updatedPerson.
Step 2: We then assign updatedPerson back to the variable person, effectively replacing the original person object with the updated version that includes the new property.

Result:#

After executing the above code, person will now be:

{
  firstName: 'John',
  lastName: 'Doe',
  age: 30
}

Notes:#

JavaScript objects do not have a guaranteed order for properties, so adding a property “at the beginning” is more about having it logically first in your code rather than ensuring a specific physical order in memory.
This approach creates a new object and reassigns it, which may not be efficient for very large objects or in performance-critical scenarios. However, for most typical use cases, this method is straightforward and effective.