To convert a data value to a number, simply call the parse() function of the Y.Number class:

YUI().use("datatype-number", function(Y) {
    var output = Y.Number.parse("123123.123");
    // output is the number 123123.123
});

Under the hood, the data value is converted to a number via +data, not parseInt(). When the resulting value is NaN, then null is returned:

YUI().use("datatype-number", function(Y) {
    var output = Y.Number.parse("$100");
    // output is null

    output = Y.Number.parse("20 dollars");
    // output is null

    output = Y.Number.parse("3,000,000.12");
    // output is null (it's the commas)

    output = Y.Number.parse(new Date("Jan 1, 2000"));
    // output is 946713600000

});