function doFormat(value) {
    switch (value) {
        case 0: return "low";
        case 1: return "high";
        default: return "unknown";
    }
}
function doParse(value) {
    switch (value) {
        case "low": return 0;
        case "high": return 1;
        default: return -1;
    }
}
var parser = new CustomParser(doFormat, doParse);
alert(parser.format(0)); //Result is "low"
alert(parser.parse("ABC")); //Result is -1
alert(parser.parse("high")); //Result is 1