A knockout.js extension for a numberic observable. Limits the numeric observable to the provided min and max range args.

ko-extension-limitedNumeric.ts

// requires knockout.js and jquery.js
// limits the numeric observable to the provided min and max range args

ko.extenders["limitedNumeric"] = (target: Ko.Observable<any>, args: any) => {
	let settings: any = {
		minValue: 1,
		maxValue: null
	};

	$.extend(settings, args);

	// create a writeable computed observable to intercept writes to our observable
	var result = ko.computed({
		read: target,  // always return the original observables value
		write: (newValue: number) => {
			if (settings.minValue && newValue < settings.minValue)
				newValue = settings.minValue;

			if (settings.maxValue && newValue > settings.maxValue)
				newValue = settings.maxValue;

			target(newValue);
		}
	});

	// initialize with current value to make sure it is limited appropriately, and return the computed obs
	result(target());
	return result;
};