Unknown Javascript expression

Question

Can someone please tell me what this javascript code does? I came across it in a jQuery routine to select table rows.

Each of the following can range from -1 to the table-row count -1:

Code:

thisIndex = [lastIndex, lastIndex = thisIndex][0] ;

Help!

It's a "tricky" way of interchanging the values of `thisindex` and `lastindex`. — Pointy, Feb 01 '23 at 15:49
You'd think you could just do `[thisIndex, lastIndex] = [lastIndex, thisIndex]` now that destructuring is a thing. — tadman, Feb 01 '23 at 15:51
Other (clearer) ways to [swap variables](https://dmitripavlutin.com/swap-variables-javascript/). — jarmod, Feb 01 '23 at 15:54

score 0 · Answer 1 · answered Feb 01 '23 at 15:54

This is one method to swap the two values inside the variables thisIndex and lastIndex without using a temporary variable.

On the RHS, there is an array of two values and [0] will return the first value.

example: Suppose

thisIndex  = 10;
lastIndex = 20;

[lastIndex, lastIndex = thisIndex]

will become

[20,10]

and then assign 20 to lastIndex, the expression returns 10 which is assigned to thisIndex

1 Answers1