The comma operator in JavaScript evaluates each of its operands. It returns the value of the last operand. Add multiple expressions using the comma operator.
The following is the syntax:
expression1, expression2, ……expression
Use the comma operator to add multiple parameters in a for loop:
for (var a = 0, b = 5; a <= 5; a++, b--)
You can also use the comma operator in a return statement. Process before returning using comma:
function myFunc() { var a = 0; return (a += 1, a); }
Above you can see the value of a will process and then it will be returned.