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";

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