The exact form and function of a comparator changes based on the comparison being made, but the capability of comparing measurements is constant.
Definition
According the Merriam-Webster dictionary, a comparator is any device that's primary function is to compare an object against the standard measurement. This is an essential function for manufacturers who must regularly meet product specifications during development. The manufacturer simply uses the device and ensures the measurements match the requirements. If the measurements do not match up, adjustments can be made before the product is packaged and shipped.
Optical
Optical comparators are devices that create a silhouette or video image of an object and display the required specifications to the user. This allows the user to visually compare the item to ensure each element meets standards for quality, shape or strength. Some machines also come equipped with controls allowing the user to make alterations to the manufacturing process if the object does not match the desired specifications.
Voltage
A voltage comparator is a device that takes electrical input and compares the positive and negative voltages to find whether they are equal or if one is higher than the other. According to the University of Nevada Las Vegas Physics department, voltage comparators can be used to convert signal waves to a form that allows counting of the hertz. Another use is found in thermostats. When the temperature changes, the voltage changes and is detected by the comparator. The comparator then sends a signal to turn the heating or cooling on, to return the temperature and voltage back to the desired setting.
Javascript
Not all comparators are devices that meet the standard definition. Javascript is a programming language used to expand the capabilities of websites and is compatible with all browsers. A comparator in Javascript is not a device or comparison to standards, but instead is a sorting function. Data in an array can be sorted and displayed in a specific order based on value by a computer run comparison of each element.