Calculate Difference Between Keyframe Values.jsx

/**
 * @name Calculate Difference Between Keyframe Values
 * @version 1.0
 * @author Kyle Martinez <www.kyle-martinez.com>
 *
 * @description Calculate the difference between two keyframe values.
 *
 * @license This script is provided "as is," without warranty of any kind, expressed or implied. In
 * no event shall the author be held liable for any damages arising in any way from the use of this
 * script.
 *
 * In other words, I'm just trying to help make life as an animator easier
 * "A rising tide lifts all boats." - John F. Kennedy, 1963
 */

(function() {
    var comp = app.project.activeItem;
    var selectedProperties = comp.selectedProperties;
    var numSelectedProperties = selectedProperties.length;
    for (var p = 0; p < numSelectedProperties; p++) {
        var selectedProperty = selectedProperties[p];
        var selectedKeys = selectedProperty.selectedKeys;
        var numSelectedKeys = selectedKeys.length;
        if (numSelectedKeys === 2) {
            var selectedPropertyName = selectedProperty.name;
            var keyframeIndexOne = selectedKeys[0];
            var keyframeIndexTwo = selectedKeys[1];
            var keyValueOne = selectedProperty.keyValue(keyframeIndexOne);
            var keyValueTwo = selectedProperty.keyValue(keyframeIndexTwo);
            var difference = Math.abs(keyValueTwo - keyValueOne);
            var message = [
                selectedPropertyName,
                "[" + keyframeIndexTwo + "]" + keyValueTwo + " -",
                "[" + keyframeIndexOne + "]" + keyValueOne + " =",
                difference];
            alert(message.join("\n"));
        }
    }
})();