KnockoutJS numeric validation function modified to allow a single period.

ko_extend_numeric.js

// Modified version of code at http://knockoutjs.com/documentation/extenders.html
// Allow a single period to pass when using "textInput" data-binding.

ko.extenders.numeric = function(target, precision) {
    //create a writable computed observable to intercept writes to our observable
    var result = ko.pureComputed({
        read: target,  //always return the original observables value
        write: function(newValue) {
            console.log(typeof newValue, newValue);
            var current = target(),
                roundingMultiplier = Math.pow(10, precision),
                newValueAsNum = isNaN(newValue) ? 0 : parseFloat(+newValue),
                valueToWrite = Math.round(newValueAsNum * roundingMultiplier) / roundingMultiplier;
 
            //only write if it changed and allow a single period at end
            if (String(newValue).indexOf('.') === String(newValue).length-1) {
                target(newValue);
            } else if (valueToWrite !== current) {
                target(valueToWrite);
            } else {
                //if the rounded value is the same, but a different value was written, force a notification for the current field
                if (newValue !== current) {
                    target.notifySubscribers(valueToWrite);
                }
            }
        }
    }).extend({ notify: 'always' });
 
    //initialize with current value to make sure it is rounded appropriately
    result(target());
 
    //return the new computed observable
    return result;
};