ConstantProperty.js

import defined from "../Core/defined.js";
import Event from "../Core/Event.js";

/**
 * A {@link Property} whose value does not change with respect to simulation time.
 *
 * @alias ConstantProperty
 * @constructor
 *
 * @param {*} [value] The property value.
 *
 * @see ConstantPositionProperty
 */
function ConstantProperty(value) {
  this._value = undefined;
  this._hasClone = false;
  this._hasEquals = false;
  this._definitionChanged = new Event();
  this.setValue(value);
}

Object.defineProperties(ConstantProperty.prototype, {
  /**
   * Gets a value indicating if this property is constant.
   * This property always returns <code>true</code>.
   * @memberof ConstantProperty.prototype
   *
   * @type {Boolean}
   * @readonly
   */
  isConstant: {
    value: true,
  },
  /**
   * Gets the event that is raised whenever the definition of this property changes.
   * The definition is changed whenever setValue is called with data different
   * than the current value.
   * @memberof ConstantProperty.prototype
   *
   * @type {Event}
   * @readonly
   */
  definitionChanged: {
    get: function () {
      return this._definitionChanged;
    },
  },
});

/**
 * Gets the value of the property.
 *
 * @param {JulianDate} [time] The time for which to retrieve the value.  This parameter is unused since the value does not change with respect to time.
 * @param {Object} [result] The object to store the value into, if omitted, a new instance is created and returned.
 * @returns {Object} The modified result parameter or a new instance if the result parameter was not supplied.
 */
ConstantProperty.prototype.getValue = function (time, result) {
  return this._hasClone ? this._value.clone(result) : this._value;
};

/**
 * Sets the value of the property.
 *
 * @param {*} value The property value.
 */
ConstantProperty.prototype.setValue = function (value) {
  var oldValue = this._value;
  if (oldValue !== value) {
    var isDefined = defined(value);
    var hasClone = isDefined && typeof value.clone === "function";
    var hasEquals = isDefined && typeof value.equals === "function";

    var changed = !hasEquals || !value.equals(oldValue);
    if (changed) {
      this._hasClone = hasClone;
      this._hasEquals = hasEquals;
      this._value = !hasClone ? value : value.clone(this._value);
      this._definitionChanged.raiseEvent(this);
    }
  }
};

/**
 * Compares this property to the provided property and returns
 * <code>true</code> if they are equal, <code>false</code> otherwise.
 *
 * @param {Property} [other] The other property.
 * @returns {Boolean} <code>true</code> if left and right are equal, <code>false</code> otherwise.
 */
ConstantProperty.prototype.equals = function (other) {
  return (
    this === other || //
    (other instanceof ConstantProperty && //
      ((!this._hasEquals && this._value === other._value) || //
        (this._hasEquals && this._value.equals(other._value))))
  );
};

/**
 * Gets this property's value.
 *
 * @returns {*} This property's value.
 */
ConstantProperty.prototype.valueOf = function () {
  return this._value;
};

/**
 * Creates a string representing this property's value.
 *
 * @returns {String} A string representing the property's value.
 */
ConstantProperty.prototype.toString = function () {
  return String(this._value);
};
export default ConstantProperty;