What is going on in this Javascript code? Is there a name for this or some place to learn more about the specific behavior illustrated?

I didn't think coding a "tuple" in JS would be valid syntax, but it seems to be. However the resulting variable definitely doesn't behave as a tuple, which is expected given JS's lack of support for them.

It's behavior seems very odd to me though.

It only gets 1 of the two values stored into it, and strangely removing the parenthesis is still valid javascript but ends up storing the opposite value into the varible

-> x = (90, 27);
<- 27
-> x
<- 27

-> x = 90, 27;
<- 27
-> x
<- 90

CodePudding user response：

Comma operator returns the last element

No tuples in JavaScript

CodePudding user response：

It is just javascript evaluating expression, when you have parenthesis () javascript will evaluate the whole expression inside the parenthesis first and then assign it to the variable since x = (1,2) 2 is the last evaluated value will be assigned to x. But if you don't have parenthesis then it evaluates step by step expression x = 1,2 the first expression it finds is x=1 and then just evaluates 2 it's as if you typed x=1; 2;

CodePudding user response：

That's not a tuple. JavaScript does not have tuples. You're simply doing

x = 90, 27

but wrapping the expression 90, 27 in parentheses. The reason why it's returning 27 is because that's the last element.