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I know that var some = []; creates a new array and var someother = {} creates a new object. So what does the () do?

Specifically, in the following code : 

var someVar = (1,2,3); //someVar equals 3

and 

typeof (1,2,3) //returns "number"

So what does the () do in the above code?

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2 Answers 2

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1

See precedences of operators.

(1,2,3)

is just

3

because the comma operator returns the last value.

The parenthesis in

typeof (1,2,3)

just prevent it to be interpreted as

(typeof 1),2,3

because the typeof operator has a higher precedence than the comma operator.

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That is a grouping operator.

It causes the contents to be evaluated as an expression in their own right. Effectively it changes precedence since otherwise the someVar = 1 would be evaluated first (instead of the result of (1,2,3) being evaluated and the result used in the someVar = ... expression.

That expression 1,2,3 uses a comma operator which evaluates as the right hand side, so it is 3.

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