Knockout extender to force a field to be an integer value within a specified range.

range.knockout.js

ko.extenders.range = function( target, intRange ) {
		//create a writeable computed observable to intercept writes to our observable
		var result = ko.computed({
			read: target,  //always return the original observables value
			write: function( newValue ) {
				var current = target(),
					newValueAsNum = isNaN( newValue ) ? 0 : parseInt( +newValue, 10 ),
					valueToWrite = newValueAsNum;

	 			if ( newValueAsNum < intRange.min ) {
	 				valueToWrite = intRange.min;
	 			}

	 			if ( newValueAsNum > intRange.max ) {
	 				valueToWrite = intRange.max;
	 			}
				//only write if it changed
				if ( valueToWrite !== current ) {
					target(valueToWrite);
				} else {
					//if the tested 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;
	};