How Can I Efficiently Add Conditional Object Members in JavaScript?

Conditional Object Member Addition in JavaScript

In JavaScript, the common practice for conditionally adding a member to an object involves an if-else statement:

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

While this method works, it can be considered less idiomatic. To achieve a more concise and flexible solution, we can explore alternative approaches.

One attempt is to use the ternary operator within the object declaration:

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

However, this approach results in an object where b is present but has an undefined value.

For a general case with multiple conditional members, we can use a more elaborate approach utilizing the spread operator and logical AND short circuit evaluation:

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

In this syntax, the spread operator unpacks the object inside the parentheses and adds it to a if someCondition is true. The logical AND operator (&&) ensures that the object is only added if someCondition is true, and the short circuit evaluation prevents the evaluation of the expression {b: 5} if someCondition is false.

This approach provides a clean and efficient way to conditionally add members to an object in JavaScript.

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