JavaScript - Comma Operator

The JavaScript comma , operator evaluates each of its operands (from left to right) and returns the value of the last operand. This facilitates to create a compound expression in which multiple expressions are evaluated, with the compound expression's final value being the value of the rightmost of its member expressions.

The comma operator has left-to-right associativity. Two expressions separated by a comma are evaluated left to right.

Example:

In the example below, the comma , operator is used to evaluate multiple expressions and returns the value of the last operand.

var x = 10;
var y = 10;
var txt;

//using comma operator
var A = (x++, x);
var B = (y+=5, y*=2, y);

//displaying result
txt = "(x++, x) : " + A + "<br>";
txt = txt + "(y+=5, y*=2, y) : " + B;

The output (value of txt) after running above script will be:

(x++, x) : 11
(y+=5, y*=2, y) : 30