JavaScript Interview Question: Why does [1,2,3,4,5][1,2] = 2?

The JavaScript expression [1,2,3,4,5][1,2] results in 2 due to how JavaScript handles array access and comma expressions.

In JavaScript, when square brackets [] are used to access elements in an array, the expression inside the brackets is evaluated to determine the index of the element to retrieve. However, when multiple values are separated by commas inside square brackets, JavaScript evaluates them as a comma-separated sequence of expressions and returns the result of the last expression.

So, [1,2,3,4,5][1,2] is equivalent to [1,2,3,4,5][2], which accesses the element at index 2, resulting in 2.

This behavior might seem unexpected at first glance, especially if you're not familiar with JavaScript's handling of comma expressions. It's essential for developers to understand how JavaScript evaluates expressions to avoid confusion and unintended behavior in their code.