What does the comma operator do in JavaScript?
comma-operator, javascript
Solution
The comma operator evaluates both of its operands (from left to right) and returns the value of the second operand.
Source: https://developer.mozilla.org/en/JavaScript/Reference/Operators/Special_Operators/Comma_Operator
For example, the expression `1,2,3,4,5` evaluates to `5`. Obviously the comma operator is useful only for operations with side-effects.
console.log(1,2,3,4,5);
console.log((1,2,3,4,5));
Problem
If I use: ``` 1.09 * 1; // returns "1.09" ``` But if I use: ``` 1,09 * 1; // returns "9" ``` I know that 1,09 isn't a number. What does the comma do in the last piece of code? More Examples ``` if (0,9) alert("ok"); // alert if (9,0) alert("ok"); // don't alert ``` ``` alert(1); alert(2); alert(3); // 3 alerts alert(1), alert(2), alert(3); // 3 alerts too ``` ``` alert("2", foo = function (param) { alert(param) }, foo('1') ) foo('3'); // alerts 1, 2 and 3 ```