What is the name of this syntax "(x, y)"?

Question

I recently read javascript code and I came across this line:

var myVar = (12,5); // myVar==5 now 

What is this weird syntax: (x, y) ?

Answer 1

Comma Operator:,

The comma operator has left-to-right associativity . Two expressions, separated by commas, are evaluated from left to right. The left operand is always evaluated, and all side effects are completed before the operand is evaluated.

Expression:

 var myVar = (12, 5); 

is equivalent to:

 var myVar = 5; 

Note that in the bracket above the expression overwrites the priority , over = , otherwise without parentheses an expression like var myVar = 12, 5 is equivalent to var myVar = 12 .
Edit: There may be the following reasons why I think you will find this expression:

• When the first expression has some side effects:

    var myVar = ( expression1, expression2); 

  expression1 may have some side effects that may be required earlier to appropriate the result of expression2 myVar , for example. var mayVar = (++i, i + j); In this expression, the incremented value after ++i will be added using j , and the result will be assigned to mayVar .

• Bug fixed or bug:
  Maybe some bug fixes or during testing instead of assigning x developer wanted to assign y , but forgot to delete ( ) before being published.

   var myVar = (x, y); 

  I also found a typo in which the questioner forgot to write the same function and instead of writing

   var myVar = fun(x, y); 

  his typo:

   var myVar = (x, y); 

  In a related question .

This is not a JavaScript link, but a very interesting C ++ link that discussed the legal / or possible use of comma operators. What is the correct use of the comma operator?

Answer 2

it is called Comma Operator, we usually use them when we want to run operator 2 in one expression, it evaluates 2 operands (from left to right) and returns the value of the second.

check it out here: comma operator

And read this question if you want to know where it is useful.

Answer 3

This is called the comma operator.

The comma operator evaluates both of its operands (from left to right) and returns the value of the second operand.

Here are some examples:

  var a = (12,3) //a =3; var b = (a+2, 2) //a=5, b= 2 var c = (a,b) // a= 5, b=2, c=2.