[Javascript][Knockout] Numeric extender

KnockoutJs Numeric Extender

ko.extenders.numeric = function (target, params) {

	var options = {
		precision: 0,
		allowNegative: false
	};
	$.extend(options, params);
	//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) {
			var current = target(),
                roundingMultiplier = Math.pow(10, options.precision),
                newValueAsNum = (isNaN(newValue) ||
								(options.allowNegative && newValue < Number.MIN_SAFE_INTEGER) ||
								(!options.allowNegative && (newValue < 0)) ||
								newValue > Number.MAX_SAFE_INTEGER)
								? current : parseFloat(+newValue),
                valueToWrite = Math.round(newValueAsNum * roundingMultiplier) / roundingMultiplier;

			//only write if it changed
			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;
};