Javascript string replace

Didn't know Javascript had regular expression support.

    var str = "abcabc";
    str.replace("a", "#");
    document.write( str );

will print "abcabc".

    var str = "abcabc";
    document.write( str.replace("a", "#") );

will print "#bcabc".

    var str = "abcabc";
    document.write( str.replace(/a/g, "#") );

will print "#bc#bc".

    var str = "ABCABC";
    document.write( str.replace(/a/i, "#") );

will print "#BCABC".

    var str = "ABCABC";
    document.write( str.replace(/a/gi, "#") );

will print "#BC#BC".