SO jQuery Fiddle

Test Fiddle mainly for SO Questions jQuery 1.4.3, UI 1.8.5

by Nick Craver

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.5/themes/ui-lightness/jquery-ui.css">

JavaScript

var stringA = ["a1", "a2", "a3", "a4", "a5", "a6"]
var stringB = ["b1", "b2", "b3"]
    
var result = [], len = Math.max(stringA.length, stringB.length);
for(var i=0; i < len; i++) {
    result.push((stringA[i] || "") + (stringB[i] || ""));
}
alert(result);