This is a simple function to add up any numbers fed into the arguments: add( 1, 2.2, '3', true, 'monkey');

add.js

function add() {

    var total = 0,
        max_decimal = 0;

    for (var i=0,l=arguments.length;i<l;i++) {

        var num = parseFloat( arguments[i] ),
            arr = ( num + '' ).split('.'),
            dec = ( arr[1] == undefined ? 0 : arr[1].length );

        if ( !isNaN(num) ) {
            if ( max_decimal < dec ) max_decimal = dec;
            total += parseFloat( arguments[i] );
        }
    }

    return total.toFixed( max_decimal ) - 0;
}