How to conditionally add a member to an object using JavaScript?

Objects are the most important data types and are building blocks for modern JavaScript. They are different from primitive data-types such as String, Number, Boolean, null, etc. But we can make these datatypes as objects by using the new keyword.

Below are the approaches to conditionally adding a member to an object which are as follows:

Using If Statment

You can use an if statement to check a condition and then add a property to the object if the condition is met.

Example: To demonstrate adding a member to an object using if statement in JavaScript.

let obj = {};
let condition = true;

if (condition) {
    obj.newProperty = "newValue";
}

console.log(obj);

{ newProperty: 'newValue' }

Using Logical AND (&&)

The logical AND (&&) operator can be used to conditionally execute code. If the condition is true, the right-hand side expression is executed.

Example: To demonstrate adding a member to an object using logical and (&&) in JavaScript.

let obj = {};
let condition = true;

condition && (obj.newProperty = "newValue");

console.log(obj);

{ newProperty: 'newValue' }

Using Spread Operator with Conditional Assignment

You can use the spread operator in combination with conditional assignment to create a new object that conditionally includes a property.

Example: To demonstrate adding a member to an object using spread operator with conditional assignment in JavaScript.

let condition = true;
let obj = {
    ...(condition && { newProperty: "newValue" })
};

console.log(obj);

{ newProperty: 'newValue' }

Using Object assign Method

Object.assign method can be used to add properties to an object conditionally.

Example: To demonstrate adding a member to an object using object assign method in JavaScript.

let obj = {};
let condition = true;

Object.assign(obj, condition ? { newProperty: "newValue" } : {});

console.log(obj);

{ newProperty: 'newValue' }

Using $.extend() method in JQuery.

This method is used to add several members to an object. The jQuery library function $.extend() is used for this method. This however does not copy undefined properties to the object.

Example: To demonstrate adding a member to an object using $.extend method in JQuery.

let newObject = $.extend({}, {
  a: conditionA ? 7 : undefined,
  b: conditionB ? 9 : undefined,
  
  // More properties as required
});

Output:

When the first condition is satisfied:

{a: 7}

When both conditions are satisfied:

{a: 7, b: 9}