November 15, 1999 - The Comma Operator

Yehuda Shiran November 15, 1999
The Comma Operator
Tips: November 1999

Yehuda Shiran, Ph.D.
Doc JavaScript

You can use the comma operator to force the evaluation of a set of expressions. Sometimes called a parameter delimiter because it is used in delimiting multiple arguments in a function call:

document.write(beerNum, " bottles of beer on the wall");

In the following example:

var a = (b = "Hello", alert("Hi"), "Howdy");

the comma operators force the evaluation of the expressions in the statement. Only the last expression is returned. In the above example, "Howdy" is assigned to a. This statement is equivalent to the following three:

b = "Hello";
alert("Hi");
var a = "Howdy";