A curious usage of commas in JavaScript

By Flavio Copes

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

I recently discovered a curious yet possibly useful thing in 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:

('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:

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

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