How to Conditionally Add Members to a JavaScript Object?

Conditionally Adding Members to an Object in JavaScript

Question: How can I dynamically add members to an object, depending on certain conditions, in JavaScript?

Initial Approach:

One straightforward approach is to use an if statement to add the member if the condition is met:

var a = {};
if (someCondition)
    a.b = 5;

Idiomatic Solution:

To write a more idiomatic and concise code, avoid using undefined as the value for conditional members. Instead, use the conditional ternary operator:

a = {
    b: (someCondition? 5 : undefined)
};

However, this approach still results in the b member being defined with an undefined value if the condition is not met.

ES6 Solution with Logical AND:

For the general case with multiple members, ES6 introduces a clever solution using the spread operator and logical AND short-circuit evaluation:

const a = {
   ...(someCondition && {b: 5})
}

The logical AND (&&) operator evaluates to false if any of its operands are false. Since undefined is false in JavaScript, if someCondition is false, the {b: 5} object is not included in the spread operator, effectively preventing the b member from being added to the object.

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