Initial pass

node_modules/jsdom/lib/jsdom/named-properties-tracker.js

@@ -0,0 +1,158 @@
+"use strict";
+// https://heycam.github.io/webidl/#idl-named-properties
+
+const IS_NAMED_PROPERTY = Symbol("is named property");
+const TRACKER = Symbol("named property tracker");
+
+/**
+ * Create a new NamedPropertiesTracker for the given `object`.
+ *
+ * Named properties are used in DOM to let you lookup (for example) a Node by accessing a property on another object.
+ * For example `window.foo` might resolve to an image element with id "foo".
+ *
+ * This tracker is a workaround because the ES6 Proxy feature is not yet available.
+ *
+ * @param {Object} object Object used to write properties to
+ * @param {Object} objectProxy Object used to check if a property is already defined
+ * @param {Function} resolverFunc Each time a property is accessed, this function is called to determine the value of
+ *        the property. The function is passed 3 arguments: (object, name, values).
+ *        `object` is identical to the `object` parameter of this `create` function.
+ *        `name` is the name of the property.
+ *        `values` is a function that returns a Set with all the tracked values for this name. The order of these
+ *        values is undefined.
+ *
+ * @returns {NamedPropertiesTracker}
+ */
+exports.create = function (object, objectProxy, resolverFunc) {
+  if (object[TRACKER]) {
+    throw Error("A NamedPropertiesTracker has already been created for this object");
+  }
+
+  const tracker = new NamedPropertiesTracker(object, objectProxy, resolverFunc);
+  object[TRACKER] = tracker;
+  return tracker;
+};
+
+exports.get = function (object) {
+  if (!object) {
+    return null;
+  }
+
+  return object[TRACKER] || null;
+};
+
+function NamedPropertiesTracker(object, objectProxy, resolverFunc) {
+  this.object = object;
+  this.objectProxy = objectProxy;
+  this.resolverFunc = resolverFunc;
+  this.trackedValues = new Map(); // Map<Set<value>>
+}
+
+function newPropertyDescriptor(tracker, name) {
+  const emptySet = new Set();
+
+  function getValues() {
+    return tracker.trackedValues.get(name) || emptySet;
+  }
+
+  const descriptor = {
+    enumerable: true,
+    configurable: true,
+    get() {
+      return tracker.resolverFunc(tracker.object, name, getValues);
+    },
+    set(value) {
+      Object.defineProperty(tracker.object, name, {
+        enumerable: true,
+        configurable: true,
+        writable: true,
+        value
+      });
+    }
+  };
+
+  descriptor.get[IS_NAMED_PROPERTY] = true;
+  descriptor.set[IS_NAMED_PROPERTY] = true;
+  return descriptor;
+}
+
+/**
+ * Track a value (e.g. a Node) for a specified name.
+ *
+ * Values can be tracked eagerly, which means that not all tracked values *have* to appear in the output. The resolver
+ * function that was passed to the output may filter the value.
+ *
+ * Tracking the same `name` and `value` pair multiple times has no effect
+ *
+ * @param {String} name
+ * @param {*} value
+ */
+NamedPropertiesTracker.prototype.track = function (name, value) {
+  if (name === undefined || name === null || name === "") {
+    return;
+  }
+
+  let valueSet = this.trackedValues.get(name);
+  if (!valueSet) {
+    valueSet = new Set();
+    this.trackedValues.set(name, valueSet);
+  }
+
+  valueSet.add(value);
+
+  if (name in this.objectProxy) {
+    // already added our getter or it is not a named property (e.g. "addEventListener")
+    return;
+  }
+
+  const descriptor = newPropertyDescriptor(this, name);
+  Object.defineProperty(this.object, name, descriptor);
+};
+
+/**
+ * Stop tracking a previously tracked `name` & `value` pair, see track().
+ *
+ * Untracking the same `name` and `value` pair multiple times has no effect
+ *
+ * @param {String} name
+ * @param {*} value
+ */
+NamedPropertiesTracker.prototype.untrack = function (name, value) {
+  if (name === undefined || name === null || name === "") {
+    return;
+  }
+
+  const valueSet = this.trackedValues.get(name);
+  if (!valueSet) {
+    // the value is not present
+    return;
+  }
+
+  if (!valueSet.delete(value)) {
+    // the value was not present
+    return;
+  }
+
+  if (valueSet.size === 0) {
+    this.trackedValues.delete(name);
+  }
+
+  if (valueSet.size > 0) {
+    // other values for this name are still present
+    return;
+  }
+
+  // at this point there are no more values, delete the property
+
+  const descriptor = Object.getOwnPropertyDescriptor(this.object, name);
+
+  if (!descriptor || !descriptor.get || descriptor.get[IS_NAMED_PROPERTY] !== true) {
+    // Not defined by NamedPropertyTracker
+    return;
+  }
+
+  // note: delete puts the object in dictionary mode.
+  // if this turns out to be a performance issue, maybe add:
+  // https://github.com/petkaantonov/bluebird/blob/3e36fc861ac5795193ba37935333eb6ef3716390/src/util.js#L177
+  delete this.object[name];
+};