# A curious usage of commas in JavaScript

> Understand the comma operator in JavaScript: wrapping expressions like ('a', 'b') evaluates both and returns the last one, a curious trick you can assign.

Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2020-07-02 | Updated: 2020-07-11 | Topics: [JavaScript](https://flaviocopes.com/tags/js/) | Canonical: https://flaviocopes.com/javascript-commas/

I recently discovered a curious yet possibly useful thing in [JavaScript](https://flaviocopes.com/javascript/), related to the comma operator.

I mostly use commas to separate properties in an object, or array items.

However I never gave much attention the usage of it inside an expression.

Take this:

```js
('a', 'b')
```

Both expressions (in this case strings) are evaluated, and this returns the last element, the expression after the last comma. In this example it returns `'b'`.

You can assign the value to a variable, like this:

```js
const letter = ('a', 'b')
letter === 'b' //true
```