There are several ways to conditionally set object properties.

Let’s assume we want to copy all the properties of the formValues object below into a user object. However, the email property should only be included if the top-level domain ends in .com.

const formValues = {
  fullname: "John Doe",
  username: "johnny_d",
  email: "hi@johndoe", // this is intentional :(
};

Spread operator

With this we first isolate the email property from the rest, test it for inclusion, and use the spread operator to copy formValues into user.

// 1. Isolate
const { email, ...otherFormValues } = formValues;

// 2. Test
const includeEmail = email.endsWith(".com");

// 3. Spread
const user = {
  ...otherFormValues,
  ...(includeEmail ? { email } : {}),
};

Using an if statement

Here, we first copy the unconditional properties from formValues i.e. fullname and username into the user object. Then we test the email for inclusion. And finally update the user object.

// 1. Copy
const user = {
  fullname: formValues.fullname,
  username: formValues.username,
};

// 2. Test
if (formValues.email.endsWith(".com")) {
  // 3. Update
  user.email = formValues.email;
}

Using the if statement method can immediately get unwieldy and ineffective because we are manually adding the unconditonal properties. To avoid this, you can map through formValues like so:

let user = {};

for (let key in formValues) {
  if (key === "email" && !formValues[key].endsWith(".com")) {
    continue;
  }

  user[key] = formValues[key];
}

Object.assign

This can seem needlessly preposterous at first glance but can be faster for larger objects.

let user = {};

for (let key in formValues) {
  if (key === "email" && !formValues[key].endsWith(".com")) {
    continue;
  }

  Object.assign(user, { [key]: formValues[key] });
}

Final verdict

I often reach for the spread method whenever I can because it tends to be more readable and deductive at a glance. However, for your use case, it is also important to consider other aspects like performance and browser support.

Typically though, you need not worry. But you probably should.