References

Beginner-friendly references for web development, with live, editable examples.

The JavaScript delete operator

Operator JavaScript All modern browsers Updated
Quick answer

The delete operator removes a property from an object. delete user.email removes the email property entirely. It returns true on success. It's for object properties only — it can't delete variables, and using it on an array leaves an empty hole rather than shifting elements.

Overview

delete removes a property from an object completely — not just setting it to undefined, but taking the key out so "email" in user becomes false afterward. delete obj.prop (or delete obj["prop"] for dynamic keys) is the operation. It returns true when it succeeds, which is almost always.

It has clear limits. It only works on object properties — you can't delete a variable, a function, or anything declared with let/const/var (those just stay). And on an array it's a trap: delete arr[1] removes the element but leaves an empty slot, so the length is unchanged and you get a sparse array with a hole. To actually remove an array element, use splice() (mutating) or filter() (new array).

For removing object properties, delete is fine, but in code that favors immutability you'll often build a new object without the key instead — destructuring the rest: const { email, ...without } = user. That leaves the original untouched, which suits React state and similar. There's also a minor performance note: deleting can deoptimize an object's internal shape, so in hot paths setting the value to undefined or using a Map may be preferable.

Syntax

delete object.property
delete object["property"]

const user = { name: "Ada", email: "a@x.com" };
delete user.email;   // user is now { name: "Ada" }

delete arr[1];        // leaves a hole - use splice() instead

Example

Live example 
<pre id="out" style="font:15px ui-monospace,monospace"></pre>
<script>
  const user = { name: 'Ada', email: 'a@x.com', temp: true };

  delete user.temp;

  document.getElementById('out').textContent =
    JSON.stringify(user) + '\n' +
    "'temp' in user: " + ('temp' in user);
  // {"name":"Ada","email":"a@x.com"} / 'temp' in user: false
</script>

Best practices

  • Use delete to remove a property from an object.
  • Don't use it on arrays — it leaves an empty slot. Use splice() or filter() instead.
  • For immutable code, build a new object without the key via rest destructuring.
  • It can't delete variables or declarations — only object properties.

Frequently asked questions

How do I remove a property from an object?
Use delete obj.property (or delete obj["property"] for dynamic keys). It removes the key entirely.
Why shouldn't I use delete on an array?
It removes the element but leaves an empty hole, keeping the same length. Use splice() or filter() to remove array items cleanly.
What is the difference between delete and setting a property to undefined?
delete removes the key, so "key" in obj becomes false; setting it to undefined keeps the key with an undefined value.
How do I remove a property without mutating the object?
Use rest destructuring: const { remove, ...rest } = obj gives a new object without that key.
= destructuring